First published in EDI Journal 4/2020, with courtesy of teamwork media GmbH & Co. KG in Fuchstal, Germany

Introduction

 Full-arch implant-supported fixed restoration is a very reliable option for completely edentulous patients. The Brånemark protocol proposes that four to six implants should be inserted in the interforaminal area to support a fixed, screw-retained restoration using an immediate or delayed loading protocol.^{1, 2} Poor bone quality and quantity, especially of edentulous individuals, means that complete-arch restorations require dental implants to be generally placed in the anterior region, and this often results in long cantilevered prostheses. The use of long posterior cantilevers can be directly related to possible overloading of the peri-implant sites.^3-5

To overcome soft bone density challenge and consequently low primary stability, different implant designs have been introduced in the market ⁶ allowing clinicians to provide implant therapy with more predictable results. ^{7, 8}

In a parallel and complementary path, Computer-aided design and manufacturing (CAD-CAM) material and chairside systems and digital workflows are increasingly being used allowing for efficient and precise treatment protocols improving patients satisfaction ^{9, 10}.

The following case report describes a successful full arch treatment with the new Straumann TLX® system restored using digital workflow. This implant hybrid design combines active engaging threads leading to more predictable primary stability as well as the proven benefits of the machined neck on soft tissues, especially in patients with periodontal disease history as demonstrated in this case report ¹¹.

Initial Situation

Fifty-one-year-old female patient, with no smoking habits, general good health conditions (ASA Cl. I) and previous history of periodontal disease which was the main factor driving the loss of the remaining teeth in the lower jaw. The patient presented to the office with the main complaint of not being able to properly enjoy meals due to pain while chewing after being restored with conventional denture subsequentially the loss of all teeth in the lower arch. Based on the positive experience with dental implants in the upper arch the patient aimed for similar solution for the lower arch.

Treatment Planning

After clinical examination and assessment of panoramic radiograph (Fig. 01), it was possible to estimate favorable dimensions for full arch treatment with dental implants. To confirm available bone dimensions and quality, a CBCT (Cone Beam Computer Tomography) was further conducted (Fig. 02). The soft tissue quality could also be favorably observed, encouraging to go on with the implant supported fixed restoration therapy. (Fig. 03)

The patient’s dental history showed the extractions occurred around 6 months prior to the assessment consultation, the CBCT was decisive to estimate a generally medium to soft bone type which would require implants with active endosteal design to ensure the desired primary stability. The patient’s periodontal history also requires this patient to receive implants which could provide stable soft tissue conditions as well as easy maintenance.

Surgical planning aimed the placement of four Straumann® TLX implants Ø 3.75 mm, RT, length 12 mm, Roxolid, SLActive positioned in the anterior region where more bone availability was present and two Straumann® TLX implants Ø 3.75 mm, RT, length 8 mm, Roxolid, SLActive bi-lateraly in the posterior region where bone height was compromised.

The patient explicitly manifested the wish for a restoration with more natural looking teeth as possible, so it was planned to have a customized prosthetic framework produced by centralized milling center (Createch® - Mendaro/Spain) and individual ceramic crowns produced by our laboratory (Proteket – Oslo/Norway) to be cemented to the framework providing great esthetics.

Surgical Procedures

Under local anesthesia and intra vascular sedation to ensure patient comfort as well as to monitor the patient’s vital signs, one continuous supra crestal incision from second molar to second molar region was done with the use of blade 15c a full muco-periosteal flap was elevated in order to expose the entire ridge as well as to expose the mental foramen. To ensure no sharp bony edges that could potentially disturb the soft tissue healing would remain, the ridge was smoothened and rounded.(Fig. 04)

In free-hand technique, the osteotomy started with the anterior sites ensuring adequate distribution along the intra foraminal space with the use of the Needle® drill to the length of 12mm followed by the Ø 2.2 mm drill. The Ø 2.2 alignment pins were used to assess the optimal tri-dimensional positioning and depth. (Fig. 05) With the alignment pins in position as reference, the osteotomy in the posterior sites were subsequently performed and at this moment all sites were assessed tri-dimensionally. The same steps were repeated with the Ø 2.8 mm drill and respective alignment pins. (Fig. 06)

With all sites ready (Fig. 07), the placement of all implants was initiated with the motor hand piece at 25RPM and finalized into its optimal position with the Straumann® surgical ratchet and Torque Control with torque values measuring above 35Ncm. (Fig. 08)

RT healing abutments with 3.0mm height were screwed onto the implant and sutures applied in order to bring the flaps together allowing soft tissue stability along the healing time in one stage approach. (Fig. 09). An immediate post-operative panoramic radiograph was also taken to ensure all implants were in optimal conditions prior to allowing the patient to return home. (Fig. 10)

With the fresh memory of how much discomfort the patient felt while using the previous prosthesis, she chose to undergo the following healing days for conventional loading without the use of any prosthetic device.

Restorative procedures

After two months, the patient returned to the office so implants osseointegration and overall healing could be assessed. With the implants absent from mobility and with outstanding soft tissue healing, we initiated the restorative phase (Fig. 11).

All healing abutments were removed (Fig. 12) and open tray impression posts were placed onto the implants (Fig. 13). Peri-apical radiographs were taken to ensure adequate seating. (Fig. 14 and 15). Dental floss was tied around the impression posts serving as a net retaining the resin applied to splint all components together in order to minimize the chances they would move during the impression procedure, potentially compromising the fidelity of the positions being transferred to the model, which could compromise the passive seating of the future framework (Fig. 16). Wax rims were also produced and properly adjusted in the mouth in order to transfer as much information as possible to the dental laboratory such as vertical dimension, buccal corridor, Spee curve and mid-line (Figs. 17 and 18).

The impression was sent together with the antagonist model to our laboratory (Proteket, Oslo/Norway) for processing. After stone cast model production, the necessary material was sent to centralized milling company (Createch®) for further processing, model scanning and framework milling (Fig. 19).

The framework followed the “Abutment Hybrid” concept, and it was designed and milled in such a way leaving the occluding part with the resemblance of natural teeth undergone crown preparation so individual single crowns could be prepared and cemented to the framework. (Figs. 20 and 21) The framework was sent back to our laboratory where it received a layer of opaque (Figs. 22 and 23) and then artificial acrylic gingiva was applied and cured onto it after thoroughly discussing with the patient how she wanted it to look. The framework was then scanned so the individual crowns could be designed and produced. The next step was to cement the (Monolithic Zirconia) crowns to the framework (Fig. 24, 25 and 26).

This type of restoration benefit is highlighted in the patient’s emotional and tactile feeling when flossing and natural esthetics. From the technical point of view, it has the advantage of individual tooth replacement in case of potential chipping instead of the burden for the patient and doctor having to produce an entire new framework.

The restoration was seated on to the abutments and the screws were tightened with a torque of 35N/cm. The screw heads were properly protected with Teflon tape and light cured composite was used to finalize and protect the access. Due to the history of periodontitis it was mandatory the restoration would provide full cleanability access. (Fig. 27, 28 and 29). A final panoramic radiograph was taken to ensure proper prosthetic seating at the day of the delivery and respectively one year after in the follow up consultation (Fig. 30 and 31).

Treatment outcomes

The patient is completely satisfied with the treatment from all perspectives. She is now able to chew with confidence her favourite dishes free from discomfort and pain, as all as self-confident when in social event not fearing the denture will fall out of her mouth at any given moment. In addition, the patient was so satisfied with the new solution for the lower jaw, that she decided to have a rework of her former implant-supported bridge on the upper jaw.

Discussion

Aiming for clinical success selecting an implant that provides adequate primary stability in the bone bed is essential. Primary stability depends on the bone quality, surgical technique, and implant design.¹² According to Wilson et al.,¹³ the proper design of the tapered implant with a screw-tapered shape provides greater stability because it applies pressure on the cortical bone at the time of installation, thus promoting a balance between compressive and tensile forces while minimizing shear force generation. It is expected that tapered implant design favours the biomechanical strength of the bone-implant interface. Currently, however, there is no consensus about marginal bone loss as a consequence of the use of tapered versus parallel walled implants, while Lee and colleagues achieved a better clinical performance with tapered implants in the posterior mandible ¹⁴.

The principle of crestal bone remodelling (saucerisation) around a dental implant has been widely noted in the literature ¹⁵. The etiology of this bone loss can vary depending on the type of implant (one-piece vs. two-piece) and also on the type of abutment especially in case of two-piece implants ¹⁶. Bone Level implant is a type of 2 piece implant with the IAJ at the level of crestal bone and uses a horizontal offset concept whereas, Tissue Level implant which was used in this case report is a type of 2 piece implant, where the IAJ is above the crestal bone, at the soft tissue level.

Studies demonstrated that moving the IAJ supra-crestally reduces peri-implant bone loss as greater amount of inflammatory cells were seen in cases of sub-crestal implant placement ¹¹.

Finally, dentists and patients can benefit from implants which design can predict the implant primary stability, especially when immediate treatment protocols are aimed. In a different perspective but also on the benefit context, tapered endosteal design in combination with Tissue Level neck design, as presented in this case report seem a promising solution.