The fast way to restore a debilitating dentition
Dr Burzin Khan, Mumbai, India
Elderly patients are often unable to eat, talk or smile with confidence due to failing or missing teeth. This adversely affects their quality of life, with poor oral hygiene, dental caries or periodontal disease triggering systemic disease. The task of the dentist is to treat failing dentitions and edentulous spaces prosthodontically, restoring the patient’s feeling of well-being and satisfaction.
Placing conventional implants to support fixed full-arch restorations in atrophic jaws is subject to anatomical limitations, such as the maxillary sinus and the mandibular nerve. Conventional implants can require extensive bone grafting, which prolongs the treatment and increases its cost. The treatment can require up to 16 months, during which the patient often has to wear a removable denture.
In 1995, Dr Paolo Maló presented the “All-on-4” concept to overcome these problems. This concept combines tilted distal implants and axial anterior implants with cross-arch splinting and immediate loading. Bredent medical, Germany, in association with Dr Georg Bayer, Landsberg, Germany, improvised the technique in 2007 with the focus to facilitate the manufacturing of the immediate temporary bridge and the variety of the definite prosthetic rehabilitation; they termed it the “SKY fast & fixed”.
Tilted implants offer surgical and prosthodontic advantages. Long tilted distal implants help provide multicortical bone anchorage without interfering with the mental foramina. In the resorbed maxilla, they are an alternative to sinus floor augmentation with resulting reduction in morbidity. Tilted implants avoid cantilever situations by placing the implants further distally, resulting in a better distribution of loads across the dental arch. This technique of tilted implants thus improves bone anchorage, reduces the need for bone grafting and has therefore been advocated by many authors a viable, minimally invasive treatment modality that meets with great acceptance on the part of patients. Strain-gauge measurements showed no significant differences in forces and bending moments between tilted and non-tilted implants. Clinical results indicate that immediately loaded tilted implants may achieve outcomes of the same quality as axial implants in both jaws. A review of prospective and retrospective studies has shown no evidence of any differences in success rates between tilted and axial implants. The marginal bone loss observed with the tilted and axial implants also proved very similar. The behaviour and prognosis of tilted implants would therefore appear to be similar to that of axial implants.
The SKY fast & fixed treatment provides for im- mediate loading on condition that the implants achieve primary stability at a torque of >30 Ncm. A slight load on healing bone accelerates its heal- ing rather than prolonging it. Immediately loaded implants do osseointegrate, provided that the forces exerted and implant micromobility are controlled (< 150 µm). Splinting the implants with the temporary bridge is therefore recommended.
BioHPP is a high-performance polymer, a ceramic-reinforced variant of PEEK (polyether ether ketone). Its modulus of elasticity is very similar to human bone (Fig. 1), meaning that it attenuates masticatory forces – unlike conventional materials which could cause ceramic fractures or TMJ problems.
Compared to metal alloys, BioHPP is very light and resistant to galvanic currents and aesthetically adapts to the oral cavity. The bond strength achieved with the PMMA and composite primer visio.link (bredent, Senden, Germany) exceeds 25 MPa, so the material can be successfully veneered with traditional veneering composites. The present article describes a full-mouth reconstruction for a geriatric patient with the SKY fast & fixed treatment concept.
Case report
A 61-year-old female patient presented in a partially edentulous state with decayed and mobile residual teeth. She wanted a fixed replacement for her teeth, with no edentulous interim treatment phase. She was not keen on additional bone grafting due to the higher cost and the extended edentulous phase this implied.
The clinical and radiological examinations revealed a chronic generalized periodontitis (Figs. 2 and 3).
There was bilateral pneumatisation of the maxillary sinuses and bone resorption in the posterior mandible due the long time that had elapsed since those teeth were lost. However, there was sufficient bone height and width in the anterior segments of the maxilla (between the right and left anterior walls of the maxillary sinus) and mandible (interforaminal region). It was therefore decided to place four implants in the mandible and six implants in the maxilla and to provide an immediate temporary prosthesis within the anatomical restrictions. The distal implants in either arch would be tilted to obtain longer implants with transcortical stabilization to withstand cantilever forces up to the first molar. Rigid cross-arch splinting would support immediate function of the provisional restoration.
Preoperative procedures
Diagnostic (working and occluding) models were made and profile pictures were taken for model analysis (Fig. 4). The existing teeth were used as a reference for the vertical support. The jaw relations were recorded using bite wax posteriorly (Fig. 5). The working models were articulated to reflect the existing vertical dimension of occlusion (VDO). A trial set-up of the teeth was performed after erasing the existing ones on the working models (Fig. 6). The decision to go with a fixed hybrid prosthesis instead of a removable one was justified, given the adequate lip support from the residual ridge.
Pre-procedural steps are also important for softtissue aesthetics in terms of locating the transition line between the prosthesis and the oral tissue. The transition line must be concealed and should therefore run apical to the smile line. Since the patient had a low lip line, no bone reduction was needed to adjust the transition line. A cone-beam CT was used to determine the right size of the fixtures (Table 1). The implant positions were planned using 3D planning software (Sky Plan X; Bredent) (Fig. 7).
Surgical procedures
The surgery was performed under local anaesthesia using the infiltration technique at multiple surgical sites (articaine with adrenaline 1 : 100,000). The mandibular teeth were extracted and the sockets thoroughly curetted. A mid-crestal incision was made and a full-thickness mucoperiosteal flap elevated. In the posterior area, the flap was raised until the mental foramen became visible and the nerve could be visualized (Fig. 8). A crestotomy flattened the ridge and provided a wide and uniform bone platform. Pilot drilling was performed for the anterior axial implants on both sides of the midline in the lateral incisor region, followed by the placement of paralleling pins. The angulation guide was placed at the position of the planned axial sites (Fig. 9). The distal osteotomy sites for the tilted implants were prepared at an angle of 35° on both sides. The bone distal to the tilted implants was contoured using the round bur so as not to interfere with the seating of the multi-unit 35° abutment. An implant insertion torque of > 35 Ncm was achieved for all four implants (Table 2). The sockets were grafted with alloplastic bone (Ossceram nano, 0.5 –1 ml; Bre- dent) and the site closed with interrupted sutures (Vicryl 4-0).
Straight 0°, 17.5° and 35° SKY fast & fixed abutments with different collar heights depending on the gingival profile were placed on the implants (see Table 2) to ensure access and relative parallelism for the rigid prosthesis to be placed passively. The abutment screws were torqued to 25 Ncm. SKY fast & fixed impression copings were placed (Fig. 10) and a closed-tray polyether impression was taken in a stock tray. SKY fast & fixed gingiva formers were placed on the implant fixtures for the provisional period (Fig. 11). With the gingiva formers in place acting as an index, a silicone wax bite was registered with the posterior teeth providing vertical support.
Laboratory procedures
The models were mounted on the articulator using the silicone check bite, and a wax-up of the mandibular teeth was made. A putty index of the original tooth profile was registered on the diagnostic model and used to provide a guideline for the labial positioning of the teeth (Fig. 12), followed by the placement of visio.lign shells (novo.lign veneers). Once a second labial index of this set-up had been taken, the wax was boiled out and the cast steamcleaned. The visio.lign shells transferred to the index were stabilized with Protemp resin, after which the lingual aspect of the prosthesis was built up. Only one titanium coping was engaged within the temporary bridge; the other three copings were bonded intraorally using Q resin and activator (Bredent) (Fig. 13). This ensured a passive fit of the prosthesis on the implants. The base of the temporary prosthesis was finished and polished after removing it from the mouth; it was given a convex shape for more efficient maintenance. The defining aspect of the temporary prosthetic design was that it did not have a distal cantilever, spanning from premolar to premolar.
Provisional phase
The temporary bridge coping screws were torqued to 20 Ncm (Fig. 14). The occlusion was adjusted to ensure anterior support and guidance. The posterior teeth were kept in light occlusal contact up to 20 –25 µm. The patient was informed about the need to avoid chewing hard food and to report back to the dental office in case of any breakage or cracks in the prosthesis. A similar procedure was carried out with six implants in the m axilla (see Table 2), namely a long tilted distal implant on each side engaging the anterior wall of the maxillary sinus and four axial implants in the anterior segment (positioned at the central incisor and canine positions) (Fig. 15).
Definitive prosthetic phase
During the healing phase, the patient was recalled once a month. After five months of healing, an open-tray elastomeric impression (VPS Heavy body with Light body) was taken of the upper and lower arch. Due to the restricted space available for the flange in the anterior maxilla and in order to avoid prominence of the upper lip, it was decided to change the multi-unit abutment for the four anterior implants with standard 15° abutments.
An open-tray implant-level impression of the four anterior implants and an abutment-level impression of the distal two implants was taken. Implant impression posts were splinted and stabilized with dental floss and FRP-Resin (light-curing; Bredent) (Fig. 16) to ensure an accurate transfer. Bite records were made using wax rims with one titanium coping engaged for stabilization. The records were correlated with the bite of the provisional model.
It was decided to provide a definitive framework made of Bio-HPP for better resiliency and less heavy loading. An aesthetic outcome was ensured by the visio.lign system and the veneers. The gingival aspect was prepared using crea.lign. To ensure retrievability and a passive fit, the maxillary prosthesis was secured with prefabricated lateral screws on the distal implants and individual lateral screws in the anterior region (Fig. 17). The anterior housing of the lateral screws were incorporated within the framework and luted and picked up intraorally using DTK adhesive resin cement and primer. For the mandibular arch, one cylinder was incorporated within the frame and the other three luted with DTK adhesive resin and primer intraorally to ensure a passive fit (Fig. 18). The small attachment screws were torqued to 18 Ncm. Minor occlusal adjustments were performed intraorally to ensure a stable canine guidance.
Oral hygiene instructions included the use of a narrow interdental brush and a water flosser below the prosthesis and recalls every three months for the first year and every six months thereafter.
The patient was very comfortable with the prosthesis and delighted with its aesthetics, as it restored her smile and confidence (Figs. 19 and 20).
Discussion
The SKY fast & fixed treatment has been successfully used in a large number of cases, achieving improvements in function, aesthetics, confidence and speech as reported by patients. The use of tilted implants has gained immense popularity as an option for implant insertion without complex grafting procedures.
A systematic review reported no significant difference in marginal bone loss around axial (0.43 to 1.13 mm) and tilted (0.34 to 1.14 mm) implants. In spite of a trend towards lower bone loss around axial implants compared to tilted ones at twelve months, as well as after three or more years of function, no significant difference could be found. Neither the location (maxilla vs. mandible), the loading mode (immediate vs. delayed), the restoration type (full vs. partial prosthesis) or the study design (prospective vs. retrospective) had a significant effect on marginal bone loss.
Another study analysed the photoelastic strain patterns surrounding distal implants placed at 0°, 15°, 30° and 45° angles. There was no significant difference in strain magnitude between models of implants placed at 0°, 15° and 30° but an increase in strain for 45° implants. The magnitude of stress and strain for angled abutments was within or slightly above the physiologic limits. The use of angled abutments on two tilted implants placed in a curved arch and with cross-arch splinting might help decrease the stresses around the distal implants.
Stresses that developed in the supporting structure were studied on photoelastic models and recorded with photographs. The results revealed that posterior tilting of distal implants splinted in a full-arch fixed prosthesis did not increase the stresses in bone around the distal implants versus the axial-implant model. The study concluded that the use of tilted implants reduced the maximum stress in the distal crestal bone of the distal implant by approximately 17 per cent relative to the axial implants.
The cantilever should be restricted to one tooth distal of the tilted implant; a guideline for size would be 1.5 times the anteroposterior spread, or an average of 10 mm in the mandible and 6 –8 mm in the maxilla, owing to the low bone density. The cantilever should be minimized, as its presence greatly increases stress on the distal implant, regardless of whether or not the prosthesis is supported by four or six implants.
Soft-tissue considerations in the SKY fast & fixed treatment concept:
- Transition line – in cases of a vertical maxillary excess, a bone reduction may be needed to adjust the transition line to run apical to the smile line;
- Adequate width of keratinized gingiva around implant for healthy peri-implant tissue;
- Immediate provisionalisation to improve soft- tissue
In the present case, the transition line ran apical to the smile line, so a favourable aesthetic outcome was ensured; also, there was sufficient attached gingiva around the implants.
BioHPP was the material of choice for the super- structure because of its superiority to conventional metal or zirconia. It is a biologically inert material, and since it can be polished to a high lustre (Fig. 21), it is very resistant to plaque accumulation and discolouration even on exposed surfaces and framework aspects.
The three-year follow-up of the patient showed no clinical evidence of marginal bone loss as assessed on the OPG (Fig. 22) as well as a well-suited gingival profile. Most importantly, the patient was able to chew comfortably and smile with confidence.
In conclusion, the standardized SKY fast & fixed treatment protocol with BioHPP as framework material for the definitive prosthesis provides immediate support to facial structures and avoids multiple grafting procedures, saving patients’ time. It provides a harmonious approach to the management of patients needing a permanent rehabilitation of their edentulous jaws and results in high patient satisfaction.