Use of Intraoral Welding to Stabilize Dental Implants in Augmented Sites for Immediate Provisionalization: A Case Report

Immediate implant insertion and provisionalization has been defined as a predictable procedure that can be enacted with no particular differences with respect to types of implants involving various morphologies and microstructural features.1–4 It is known that immediate-loaded multiple implant systems perform better than immediate-loaded single implants. The reduction in intensity of all occlusal and nonaxial forces can only be achieved when 2 or more implants are joined together. Intraoral welding units have been used for years5 to weld titanium frameworks to abutments to allow immediate loading on implants inserted in edentulous jaws.6,7 Welding the implants together leads to a different mode of distributing the stresses acting on the structure; the implants no longer act individually, but rather, they participate in a joint effort in providing mechanical support for the prosthesis.

The most immediate concept when attempting to imitate the function of an organ is to imitate its form and structure. In practice, however, this is not possible. Therefore, when attempting to reproduce the tooth, it is natural to use the concept of a tooth, that is, a monoimplant. How would an engineer attempt to compensate for the lack of gomphosis?

Gomphosis is a system that perfectly absorbs the functional stress in completely healthy conditions. This mechanism is absolutely necessary, not only as a means of discharging stress but also to compensate for geometric and structural alterations of the jawbone. All of this constitutes a mechanical system comprising the “prosthesis implant structure – bone.”

The three units (prosthesis, implant, and bone) are all subject to occlusal and nonaxial stresses, and each reacts in its own way. Even if more expanded and controlled investigations over longer time periods are necessary to better determine the long-term success of provisional stabilization by intraoral welding, it can be a suitable procedure to achieve stronger stability during healing in order to break down nonaxial forces enacted, for example, by the tongue, orbicular muscle of the lips, and buccinator muscle. Adapting this approach of provisional stabilization by intraoral welding (a type of orthopedic splint upon implants) to immediate loading in augmented areas represents further procedural progress when more surgical time can be scheduled.

Bone resorption in the anterior maxillary edentulous areas is an important consideration that affects the choice of implant diameter and position, and the choice may not be ideal for the teeth to be replaced. The result might be a failing position or a smaller diameter than necessary. Another failed outcome is an insufficient esthetic aspect of the tooth-gingiva architecture, which may be resorbed in the “washboard” form of a flattened alveolar bone.

If bone graft techniques are not considered, the first option is thickness augmentation by separating the cortical bone walls, thus creating a space that can be filled with bone or bone substitutes, or can be left open using implants as space-keeping devices. In all cases, no load has to be applied to the area.8 The split-crest technique is undoubtedly an advantageous procedure to obtain the correct alveolar bone thickness in resorbed edentulous ridges, while at the same time avoiding bone grafts from donor sites, reducing morbidity for a second surgical area, and diminishing the size of incisions at the first site. The split-crest technique takes advantage of the growth potential of bone when it undergoes osteogenetic distraction and has a similar healing pattern to extraction sites.9 

Because the space between the 2 cortical bone plates does not contain mature bone, standard protocol allows healing and maturing before implant placement. There are a lot of modifications to this technique regarding bone substitutes or direct implant positioning to avoid the direct load on the area.9 All of these modifications need a longer healing time and often do not allow use of a temporary prosthesis to improve provisional esthetics.

Herein we suggest that by using an intraoral welding technique it is possible in esthetic areas and selected patients to place immediate-loaded implants, thus avoiding a second surgical time, eliminating the discomfort of wearing movable temporary prostheses, and granting a suitable primary stability to immediate-loaded implants.

Sinus-floor elevation can be achieved by performing different procedures with respect to the increase in bone to be obtained and the remaining alveolar ridge and the biomaterials to be used. In all cases, an immediate load has to be avoided. Recent reviews have shown the total suitability of sinus-floor augmentation using osteotomes via transalveolar bone if compared to nonaugmented sites.10,11 

The mean value of the remaining alveolar bone in an 1-year retrospective study ranged from 6.3 ± 0.3 mm, with a mean value of augmentation of 4.4 ± 0.2 mm.12 In this study, 53 implants were placed after a sinus lift performed using an osteotome technique. The implants were not loaded immediately.

A systematic review has demonstrated how few data can be gathered regarding sinus-lift procedures to statistically evaluate and define a procedure, a biomaterial graft, and the micromorphology of implants that is better than others.13 It is important to note that no clinical trial or case report has evaluated or shown the possibility of loading a multiple implant system placed in an augmented sinus during the same surgical time.

Mechanical quiescence is a fundamental premise for the development of osseointegration around any type of implant embedded in an osseous structure. Although this fact has been regarded as dogmatic and of absolute importance until recently, it is now the subject of critical revision. More recently, the importance of this new implantology on which the structure can be loaded in a short time has been acknowledged.

Both of these opposite viewpoints contain risks and benefits that are far from negligible. It is worth recalling that the forces inside the oral cavity are considerably intense, exposing the supporting bone structure to a positive risk of transformation according to the laws of Roux and Wolff. If it is true that during bone distraction it is possible to obtain the correct new bone formation, it could be equally possible to obtain osseointegration using a titanium splint as an orthopedic guide that keeps the implants still, even if loaded in augmented areas. In multiple implant positioning, provisional resin restorations were fit to avoid micromovements on immediate-loaded implants, thus creating a system that is stronger than single implants. Why not use a titanium framework temporarily welded to all implants and create an even stronger structure? Moreover, other procedures use a similar concept: the framework is blocked among the abutments using mini-screws, which represent the weak link of the structure. In fact, the loosening affects the whole system, thus creating instability. This setback cannot affect the welding procedure. Someone could object that the springback of the titanium bar could affect the bone elastic modulus and induce a sort of orthodontic movement during the healing time, thereby affecting osseointegration, but this is not possible when osseointegration has not occurred yet, because the elastic force is dissipated by the whole framework over immature bone-implant interfaces. When osseointegration occurs, the springback will be already run out.

This experimental clinical procedure was performed in the Department of Oral Surgery of the University of Foggia in southern Italy. Forty-eight implants were inserted in 16 patients and distinguished using split-crest or sinus augmentation techniques. Different kinds of implants were used, as follows: 1 piece, 1 stage (1p1s; Futura Sas, Carpenedolo, Brescia, Italy), 2 pieces, 1 stage (2p1s, transgingival form; AoN, Due Carrare, Padova, Italy), and 2 pieces, 2 stages (2p2s; Sweden & Martina).

Persons who needed split-crest treatments were screened to select suitable patients. Inclusion criteria were nonsmoking habits, absence of active or chronic pathologic processes, no occlusal traumatisms, and parafunctions. Ten persons (7 men and 3 women; age range, 39–67 years; mean age, 50.1 years), were chosen to undergo split-crest and immediate loading of implants in esthetic areas. Twenty-seven implants were placed.

After collecting anamnestic records and informed consent, all patients accepted an oral antibiotic prophylaxis for 6 days consisting of amoxicillin (875 mg) + clavulanic acid (125 mg) twice per day, starting 2 days before the intervention. All cases involved upper incisors with a mean alveolar bone thickness value of 4.2 mm. In each case, a single crestal incision involving gingival papillas of adjacent teeth was performed, avoiding releasing cuts, except in 1 case in which, after cutting, only the crestal margin of the incision was exposed. This was necessary to approach the crest to be augmented without completely removing the periosteal coverage. The crestal bone surface underwent a piezoelectric cut using an OT7 insert of a piezoelectric surgical device (Piezosurgery, Mectron, Carasco, Genova, Italy) at a mean depth of 10 mm; the longitudinal cut stopped 2–3 mm mesially to adjacent teeth so as not to involve the periodontal ligaments. At both ends of the bone incision, releasing cuts were enacted to mobilize the buccal wall. The buccal plate was expanded using screw-form distractors placed in the same position and angle of the implants; these screw-form devices are conic and have a working end that allows penetration so that burs do not need to be used and the procedures is less traumatic. Expansion was enacted manually using increasing diameters of expanding screws.

In the case presented herein (Figure 1a through d), because the chosen implants were 5 mm in diameter and 13 mm long, the expansion was obtained using 2 screws ranging from 2.6 to 4.2 mm in diameter and 12 mm long. Implants were conic, large thread, and 1p1s² with no gap between the fixture and the abutment. Implant insertion was performed, replacing each expanding screw by an implant. Implants were positioned manually according to the prosthetic guide. Polyester multifilament stitches were placed to oppose the margins of the soft-tissue incision and to form a barrier for the resin and cement of the provisional crowns.

After suturing, a grade-4 titanium bar was welded horizontally among the implants to the palatal surfaces of the abutments using an oral electrowelder device (Figure 2a and b). Provisional incisors were set on the linked implants and cemented. No specific instructions were given. On the 10th day, the sutures were removed (Figure 2c). On day 47, the titanium bar was removed (in all cases the removal was determined arbitrarily by the operators at different time intervals) and a better fit for the temporary crowns was achieved (Figure 2d). Two weeks later, definitive dental impressions were obtained to create zirconium copings and the final restorations (Figure 3a and b). The follow-up was scheduled at 24 months.

The same inclusion criteria were applied to select 6 persons (4 men and 2 women; age range, 43–56 years; mean age, 49.6 years) who needed sinus-floor augmentation, and accepted 21 implants. After discussing the risks and benefits of the experimental technique, all participants signed informed consent to the procedure.

An oral antibiotic treatment was given, consisting of amoxicillin (875 mg) and clavulanic acid (125 mg) twice per day for 10 days. A crestal incision was drawn in the mucosa involving the distal aspect of the last tooth and extended distally for 2 cm. Two releasing cuts at the ends of the buccal aspect of the flap allowed exposure of the bone surface. In the case presented, 3 1p1s implants were placed in the premolar and molar positions in the right maxilla. Premolar implants were 4 mm in diameter and 13 and 11.5 mm long; the molar implant was 6 mm in diameter and 10 mm long. The remaining alveolar bone in the lower part radiographically measured 2.8 mm. The first 2 sites for premolars were drilled using a 3-mm external diameter trephine. The third lead hole was created in the same way, but the trephined bone was pushed up with a convex bone compactor (Figure 4a through c). The recovered bone from the first 2 holes was compacted in the third hole. A further filling was achieved using collagenic sponges to increase the elevation of sinusal membrane. Implants were manually placed, and the abutments were welded together in the palatal aspect using a grade-4 titanium bar and finally modified to accept a provisional resin bridge. The patient was discharged with no specific instructions. Staggered panoramic X-rays were done in 7 months to verify the increase in bone (Figure 5a through e). The final restoration was placed 5–7 months after surgery.

Of 16 patients, 10 underwent the split-crest technique and 6 had sinus-floor augmentation. Follow-up was done monthly for 24 months. Because the titanium framework guaranteed a strong stability during healing time, the outcome and eventual osseointegration could be evaluated only after removal. Removal time changed from patient to patient and at the discretion of the operators; it ranged from 31 to 60 days for the split-crest technique and from 4 to 7 months for the sinus-lift procedure (Table). The only parameter initially considered to be decisive by the operators was the resonance frequency of each implant obtained by Periotest. The presence of the titanium framework induced a false outcome so that this device was considered useless with respect to removal time; thus, remotion was arbitrarily decided. With respect to the split-crest technique, none of the 27 implants failed. With respect to the sinus-lift procedure, only 1 of the 21 implants failed after the titanium bar was removed 4 months after surgery: it was immediately replaced by a larger implant that was not welded to the other implants. In the failed site, the bone walls were probed to verify their consistency before placing a larger implant. No other setbacks occurred. No clinical measurement was obtained to evaluate osseointegration of the implants. The overall 2-year survival rate was 91.7%, that is, 100% in the split-crest group and 83.4% in the sinus-lift group. The procedure, explained herein, schedules the insertion of 2 or more implants, placed after augmentation techniques and welded among themselves, by an intraoral welding unit, to a titanium bar and immediately temporized; the same results were achieved using transgingival (2p1s) and biphasic (2p2s) implants.

With respect to the split-crest related procedure, in some cases, the cortical plates were thick and solid, but micromovements were unmistakable because implant restorations involved the upper central incisors and their ability to engrave food. Because it is quite difficult to divert food incision to other teeth when such central teeth are involved in restoration, it was decided to use intraoral welding to stabilize these implants. The need for splitting in these cases was due to the horizontal resorption of the alveolar wall affecting, this way, the position and direction of fixtures if related to the lower teeth. The aim of this article was to highlight a new implant procedure involving an intraoral welding unit to stabilize implants during the healing time. This procedure needs an in-depth examination in case-control studies to evaluate whether a significant difference exists in reliability and if other parameters, such as peri-implant pocket depth or bleeding on probing, may present interchangeable values if compared to standard protocols.

As to the challenges with the bar placement in all aspects of dentition, there were no troubles, thanks to the different shapes the welding unit's electrodes, which allowed the operator to reach any point in the mouth. No trouble was highlighted with respect to the welding procedure. It was safe in all cases: electric resistance welding is a procedure using pressure in which the heat required to bring the immediate surfaces to melting or forging temperature is provided by electrical resistance created by the transition of an electric current through the joint zone. Spot welding is performed without additional metal. The current passing through the electrodes generates an intense heat in the various sections that varies in relation to the resistance encountered, according to Joule's law. It is also worth remembering that, owing to the different thermal conductivity of titanium and copper used to construct the welding electrodes, no heat is transmitted to the peri-implant bone structure. In fact, copper electrodes are the preferred method of dissipating the heat generated by the electrical impulse (250/300 milliseconds).

Is it possible to load implants in augmented areas to reduce treatment time and give better comfort to patients who otherwise should wear resin partial dentures or nothing at all for a longer period? The idea for this case report is due to a procedure that involves using an intraoral welding unit to connect implants by a titanium bar over which a final restoration is inserted.5 There is no interest in leaving the bar up to the final restoration and beyond,14 but using such as an orthopedic splint on the implants could help during healing time by allowing implant primary stability and immediate loading on provisional restorations. The bar was removed at different times and at the discretion of the operators with no clinical rationale, but according to radiographs. A full clinical trial is in order to evaluate marginal bone loss, osseointegration, and other clinical measurements (Periotest) in case-control studies.