The fourth article in a series of six by Dr. John Moorhouse, Dr. Frances Trainer, and Colin Dean begins by advising dentists and technicians on this challenging protocol with laboratory notes and suggestions to assist with the temporary bridge preparation

During the surgical phase, the technician must be present to observe the positions of the fixtures, the level of bony ridge around and between them and the depth of the overlying soft tissue. Using a pencil to mark the implant sites on the prepared model (Figure 1), we adjust one of the special trays to accommodate the impression copings to the actual position of the implants.
As soon as the impression is removed, it is washed and dried with a three-in-one syringe. Tags of impression material that have penetrated the flap–or gone down the side of the abutment–are removed with a scalpel. Undercuts around the impression copings are minimally filled with a new mix of 3M™ ESPE™ Impregum™ to prevent the model from fracturing when the impression is removed (Figures 2 and 3). It is then disinfected and taken for casting.

Multi-unit abutment analogs are secured to the impression copings (Figures 4 and 5), and a simple plaster of Paris model is made. As this work is not generally performed in a fully equipped laboratory, care must be taken to trim the plaster model by hand before it becomes too hard for manual reduction. The impression is removed once the plaster has set. Overhanging plaster around the replicas is carefully trimmed with a scalpel to ensure that all the registration aids seat properly (Figures 6 and 7).
The registration must be prepared so that it fits accurately onto the registration aids. The palate is removed from the upper denture and the majority of the Impregum™ is discarded as only the area that will seat on the head of the aid is required (Figure 8).

Sighting channels are cut into the palatal/lingual side of the registration and denture to ensure that only the Impregum™/aid area is in contact during seating (Figure 9). The denture flanges are relieved labially and palatally if they impinge on the model and prevent seating. At this stage, the crest of the ridge between the replicas on the model is trimmed to reflect the depth of soft tissue overlying the bony ridge in the clinical situation. This is usually 1-2 mm but can be as much as 3-4 mm if there has been a substantial amount of bone reduction. Care must be taken not to overtrim the plaster ridge as this may lead to crushing of the tissues onto underlying bone when fitting the bridge at the end of the day. This is why the technician is invited to inspect the ridges just prior to closure. Conversely, under-trimming will lead to early spaces appearing under the bridge as the area heals.
The case can now be mounted against the previously articulated opposing model. Our own preference is to use Craft Match splints from Tesco with Azobond cyanoacrylate with activator spray from Adhesive Brokers (Figure 10).

Flat edges should be ground on the labial flange and palatal edge to ensure accurate location and support of the bridge against the sulcus of the model by using lab putty matrices once the aids have been removed (Figures 11 and 12). A perpendicular channel is drilled through the fitting side of the bridge (the long axis of the transfer aid) into the center of the imprint of each transfer aid with a No. 2 rose head bur (Figures 13 and 14). The remaining impression material is then removed from the temporary bridge.

A temporary mult-unit coping is placed with a 20-mm guide pin onto one of the analogs (Figure 15). The channel is then progressively widened to allow the bridge to seat back onto the putty matrix with sufficient clearance to allow the later introduction of the acrylic resin. Excess length of coping is removed to 2 mm below the finished surface of the bridge (Figure 16). The same procedure is repeated for the other three copings.

The plaster model is coated with cold mold seal as a separator for the acrylic resin. Rubber separator is painted over the long screws to facilitate removal. Self-curing acrylic resin is then poured into the anterior channels to attach the temporary copings to the bridge. Ideally this is completed with a single mix, although two or three applications may be required. When full, the case is transferred to a hydroflask for processing in warm water for 4 minutes. The mix is introduced to the anterior channels and allowed to fill them completely, whereas the posterior channels are topped up with dentine/tooth colored acrylic for a more esthetic occlusal surface (Figure 17). The silicone matrices are removed and a final mix is applied to the edges of the flanges to ensure there are no gaps on the fitting surface before trimming; this is then processed.

The guide pins are now removed and the model is returned to the articulator, where excess acrylic, which would prevent occlusion, is removed. The bridge is carefully separated from the model before trimming begins (Figure 18).
The bridge is trimmed and polished to form a convex surface to oppose the convex surface of the ridge. An exception to this is if a small ridge lap may be necessary to hide the metalwork of an abutment.

Tooth trimming at the gingival margin should be avoided because this can lead to food debris becoming trapped and causing staining, which is difficult to remove in a fixed-bridge situation (Figures 19 and 20).The case is then returned to the articulator (Figure 21) to check the occlusion and for final grinding before being returned to the surgery in a bath of chlorhexidine ready for fitting.

Fitting the temporary bridgework
The thorough planning from the outset, the accuracy of the Lymm registration technique, and careful surgery preparation should make fitting the temporary bridge a relatively straightforward procedure taking less than 20 minutes. We first test the mucosa around each abutment for tenderness. The patient’s response determines whether we continue without anaesthesia, treat sensitive areas with topical anesthetic (Ultracare® gel benzocaine 20% w/v, Ultradent®), or infiltrate with lidocaine hydrochloride.
A general restorative kit (Figure 22) is prepared with a set of four lengths of Nobel Biocare® drivers, a multi-unit driver for straight abutments and a torquing device. It is a good idea to check that the driver length is long enough to pass through the acrylic build-up of the bridge and reach to the bottom of the temporary abutment to engage the screws into the multi-unit abutment in all four access holes.


  
The temporary covers are removed and the bridge is seated onto the multi-unit abutments, taking care not to trap soft tissue between the metal components. The bridge should be held firmly until all four screws are in place to avoid overstressing either the implants or any of the prosthetic components. A paper towel from the sterilization kit is kept handy to maintain dry fingers and a positive contact with the small components and drivers. The screws are tightened to 15 Ncm, the first notch on the manual torque wrench, and this must not be exceeded. The bridge is brought into occlusion with the opposing arch and the closed vertical dimension is checked using the Willis gauge and the marks on the nose and chin.

The occlusion is finessed, and the holes are sealed with cotton pledgets and composite. The patient is then raised to a sitting position, and the smile line and phonetics are checked. Small adjustments are still possible, and the patient can admire his/her new teeth in a face mirror (Figure 23).

The guardian is now invited into the surgery, and post-implant placement and post-sedation instructions are given and discussed. The need for a soft diet for 4 weeks is stressed, and the patient is warned of the possibility of swelling and bruising.
All the laboratory work and documentation is collated and retained (Figure 24). A letter containing a copy of the surgical notes is sent to the referring dentist (and restoring dentist, if different).  

Review and monitoring
Both the implants and the temporary bridge need to be monitored pending the completion and fitting of the definitive bridge. Monitoring and follow-up treatment are carried out at three regular appointments. The accessible sutures are removed after 1 week. The soft tissue is checked for healing, and the occlusion is finessed if necessary. The patient is again reminded of the need for a soft diet for a further 3 weeks, and cleaning instructions are reinforced. We advise the use of a denture cleaning paste on a soft brush to prevent abrasion and loss of esthetic surface finish. Chlorhexidine mouth rinses are continued if there is any sign of inflammation. On rare occasions, it may be necessary to prescribe further antibiotics.



When the patient returns for review after 1 month, we would expect the soft tissue to be completely healed. The patient is introduced to cleaning where possible under the bridge with interdental brushes and/or Super Floss® (Oral-B®). He/she is advised that their diet can now include slightly harder foods and is encouraged to introduce these progressively over the coming weeks until the next appointment.

After 2 months, the patient’s observations and satisfaction with the procedure to date are recorded. Comments on esthetics and phonetics are noted and may prompt design changes in the definitive bridge. The patient is asked to find photographs from when he/she had natural teeth and to take them to the first appointment with the restoring dentist. A periapical radiograph is taken of each implant using a Hawe Neos or Rinn holder to deliver baseline information on the level of bony integration of each implant. The radiographs will also show the accuracy of fit of the abutment and the temporary cylinder (Figure 25). The occlusion is checked and adjusted if necessary. The cleanliness of the bridge is assessed, and instruction and encouragement offered where needed.

The bridge is then removed, cleaned in an ultrasonic bath, and the underlying soft tissue is checked for signs of inflammation. The fitting surface of the bridge is adjusted and polished where necessary. The abutments are washed and then irrigated with a chlorhexidine spray. Replacing the bridge and sealing the access holes with cotton and composite completes the management of the temporary bridge. A preliminary appointment is then made to begin construction of the definitive bridge in 2 months time.
The patient is given the box containing all the laboratory components and documentation, and a final letter of completion of treatment is written to the referring and/or restoring dentist(s). The letter should include a report on the periapical radiographs, the patient’s esthetic and functional requirements, and helpful information on his/her response to the procedure so far.  

Complications
The final section of this article deals with the complications we have encountered as our experience with All-on-4™ has evolved–some of which we now know to have been preventable–and their solutions. Medical complications such as high blood pressure or liver impairment make it more important to monitor and reduce the toxic load of the local anesthetic wherever possible. The load can be reduced if surgery is performed on one side at a time.

Excessive bleeding during surgery can prematurely wash away local anesthetic. This is relatively easy to overcome in the lower jaw with an ID block and infiltrations, but is more of a problem in the maxilla when extensive flaps have already been reflected. In these instances it is usually possible to deposit local anesthetic as an infiltration in the palatal mucosa in the premolar region about 5 mm from the midline. This complication often can be prevented with prompt identification of bleeding points and adequate finger pressure.



Fitting the temporary bridge is the culmination of weeks of preparation and a hard day’s work. A badly contoured bridge fitting surface can lead to the crushing of soft tissues onto the bony ridge and a great deal of pain at fitting. This can ruin what should be a satisfying result for all concerned. It is essential that the technician trims the model accurately according to his/her observation of the levels of bone and soft tissue between the implants during surgery.

There is often a large bulk of anterior palatal mucosa after significant ridge reduction, which can irritate some patients. The patient can be reassured that this always resolves within the first 3 months. We have had several cases where the implant rotates while the abutment is being tightened. Experience helps in adapting the drilling protocol to achieve the best possible primary stability of the implant to prevent this happening. A lower abutment torque should be accepted if it is already well seated on the implant, and a note made in the clinical record. The abutment will be re-torqued to the correct tension prior to the impression appointment for the definitive bridge. If the abutment is not sufficiently firmly seated, it is possible to increase the torque by simultaneously holding the abutment guide pin to prevent rotation.

Patients with an upper temporary bridge often find they are lisping due to the unfamiliar bulk of acrylic palatal to the upper incisors. It is possible to reduce this bulk, even to an absolute minimum, provided the reduction does not compromise the strength of the bridge itself and lead to fracture. We try to manage this problem by reassurance that the bulk can be dramatically reduced with the definitive bridge and that it is only a short-term problem with the immediate bridge. We encourage the patient to practice speaking by reading aloud, and this is usually successful within a few weeks.

Occasionally, we encounter patients who expose a great deal of premolar ridge when they smile and who also have large sinuses, making it impossible to trim the ridge crest to hide the acrylic/mucosal junction. In these cases, the gum work must not only be ridge lapped to hide the junction but also be designed, and the patient so taught, to be cleansable by the patient using Super Floss™. In extreme cases, this may be a contra-indication to the application of the All-on-4™ technique, and as such should be identified during the preliminary examination.

If the bone has not been adequately cleared around the implant head, the abutment can sometimes only appear to have sat down cleanly and been torqued correctly. This discrepancy will be evident on radiographic examination at the 2-month review and presents as a small gap between the implant and abutment, which is clinically loose. The area should be irrigated with chlorhexidine and the abutment torqued down correctly. The temporary bridge can be replaced, but the abutment screw on this implant must not be replaced, or intolerable stress will occur on the bridge and implant.

It is not uncommon for the small screws fixing the bridge in place to fracture if they are even marginally tightened beyond the recommended 15 Ncm. If this happens, the remaining screws need to be removed along with the bridge to access the abutment holding the threaded portion of the broken screw. These remnants will sometimes unscrew with repeated small anti-rotational movements with the tip of a probe, although this can take some time. Sometimes a small lip of metal remains that can be engaged and the remnant unscrewed with the appropriate sized excavator. In the event it proves too firmly lodged, it can be drilled out with a ½ round tungsten carbide bur, taking great care not to damage the screw threads of the abutment itself. The patency of the threads of the abutment can be tested with a new screw and the bridge replaced if this operation is successful. If the threads have been damaged, the abutment will need to be replaced; refitting the guide pin prior to removal will ensure the correct angulation is maintained.

Occasionally, temporary bridges may suffer fractures of the acrylic teeth or through the body of the bridge–usually at the weak point of the abutment. Tooth fractures are usually due to bruxing but can be caused by occlusal interferences or a contaminated bond between the tooth and the acrylic. Matrix fractures are related to the thickness of the acrylic bridge, which is a function of the available inter-maxillary space.
 
Both types of fracture should alert the prosthodontist to potential problems with the definitive bridge, although temporary bridge fractures can easily be repaired by removing it and fixing it to the model for stability while the work is carried out.
However, if a temporary bridge suffers repeated fractures, we try to expedite the conversion process as soon as possible after a minimum period of 2 months. Temporary bridge body fractures indicate the use of a titanium frame with composite teeth and gumwork for the permanent prosthesis.

In one case of a particularly aggressive bruxist, it was necessary to produce a titanium frame with full palatal coverage (Figure 26). Fortunately, we had anticipated occlusal problems in this case and were able to place six supporting implants.

 

Bios
John Moorhouse BDS, DDH, MFGDP, DPDS, Dip Implant Dent RCS Eng, was awarded a BDS at Manchester University in 1978, winning the prize for periodontology.

He has spent many years in the NHS and private practice providing the full range of skills required of the modern dental practitioner.

He has worked extensively abroad establishing dental clinics in Zaire, Thailand and Malawi. He was the lecturer in oral health for the School of Medicine in the University of Malawi and has published several research papers on oral health and health education. He was awarded a Diploma in Dental Health for Educators, DDH, in Dublin in 1989 winning the Presidents prize.

He was awarded the diploma of membership in the Faculty of General Dental Practitioners of the Royal College of Surgeons MFGDP, in 2001. He also gained the diploma in postgraduate dental studies, DPDS, in 2001 involving children’s dentistry, denture design and provision, and the management of tooth wear. John was one of the first groups of dentists to be awarded a diploma in implant dentistry and has been a tutor on the course ever since.

Frances Trainer BDS, FDS RCS (Eng), qualified in Dundee and after postgraduate posts in London and Edinburgh, gained her fellowship from the Royal College of Surgeons, England. She has spent the last 20 years in general dental practice, the last 10 years in Lymm with John Moorhouse, where restoration of dental implants has become a major part of her clinical work. She has been involved with undergraduate teaching at The Manchester Dental School and is currently a postgraduate tutor for the Manchester and Stockport areas. Frances is also a clinical support advisor for Oasis Healthcare, and a regional clinical services advisor at Oasis.

Colin J Dean, FBIDST, Dip RCS (Eng), qualified as a dental technician in 1966 and has spent many years completing both NHS and private prosthetic and crown and bridgework. He worked for a time at Birmingham Dental Hospital before taking up a post as senior lecturer in dental technology at Manchester Polytechnic.

He became co-owner of Bolton Dental Laboratory in 1979 and was awarded fellowship of the British Institute of Dental and Surgical Technologists in the same year. Colin further qualified as a clinical dental technician in 2003 while working as a senior dental technician at Manchester Dental Hospital.

In 2005, together with his son Jonathan, Colin opened C&J Dental Technologists Ltd where they specialize in implant-retained prostheses. The business also incorporates a surgery where they see patients directly for the provision of dentures. Colin is an occasional lecturer in dental technology at Manchester Metropolitan University.