Fiber-Reinforced Hybrid Prosthesis Veneered With Composite Resin for 4 Implant–Supported Fixed Provisional and Definitive Restorations Open Access

Immediate loading with provisional restorations following implant placement has become a routine protocol in full mouth rehabilitation of edentulous patients. Immediate loading protocols provide several advantages, such as (1) enhanced tissue healing, (2) improved patient comfort,¹  (3) immediate restoration of mastication and esthetics, (4) reduction of rehabilitation time, and (5) treatment costs.^2–5  The passive fit of the provisional restoration with immediately loaded implants is crucial because implant micro motions that exceed 100 μm may result in fibrous tissue encapsulation instead of bone formation.^1,6,7  For immediate loading protocol, initial insertion torque of 30–50 Ncm and rigid splinting of the implants are mandatory.^1,6,8 

Immediate full-arch provisional restorations should have a narrow occlusal platform, flat cusps to minimize lateral forces, and symmetrical distribution of occlusal forces with no cantilever extensions to avoid nonaxial implant loading.⁹  Such restorations may be cemented or screw-retained. The screw-retained type is preferred because it has the ability to remove the prosthesis at any time for servicing, suture removal, evaluation of soft tissue healing, and measuring implant stability during the healing period without causing any micro movements.¹  Also, it can accommodate diversions between implants and has no problems of excess cement.¹⁰  Several techniques and materials can be used in the construction of immediate full-arch implant-supported provisional restorations.¹¹  Early methods involved modification of a preformed complete denture and converting it to a screw-retained full-arch bridge after pick up of the temporary caps using cold-curing resin material.^12,13  Another approach is to make an impression and construct a provisional acrylic bridge, which can be connected and refitted to the implant abutments.^10,14  However, these techniques have several shortcomings such as long chairside time, heat generation to the implant area from curing of material, tissue toxicity from the residual monomer, and increased possibility of prosthesis fracture due to extensive modifications and absence of reinforcement of the denture base or the acrylic bridge.¹²  Moreover, prosthetic failures may occur due to prosthesis fractures, screw loosening, and detachment of prosthetic elements.^4,15–18  In addition, the acrylic material used in the construction of professional restorations may be subjected to wear and change in occlusion, especially in patients with natural opposing teeth that may increase the magnitude of occlusal forces.¹⁹  This article describes the use of a fiber-reinforced hybrid prosthesis veneered with composite resin for provisional and definitive (final) rehabilitation of 4 implants in the edentulous maxilla. The described prosthesis addresses several drawbacks of the conventional professional restorations. Also, it can be converted to a definitive prosthesis after minimal modifications.

The fabrication of fiber-reinforced immediate hybrid prosthesis was constructed as follows:

1. Add gutta-percha markers to the maxillary complete denture to be used as a radiographic template.

2. Make a cone-beam computerized tomography (CBCT) scan (i- CAT Vision, Imaging Sciences International, Hatfield, PA) using a dual scan protocol (1 scan for the maxillary denture alone and 1 scan for the patient while wearing the maxillary denture).

3. Plan implants according to the all-on-4 protocol²⁰  in the area between the maxillary sinuses using accompanied software (OnDemand 3D, CyberMed Inc, Seoul, Korea, Figure 1).

4. Print a tissue born stereolithographic surgical guide using rapid prototyping technology (In2Guide).

5. Fabricate a silicon cast with stone base for the maxillary denture. Pour the ridge area and the palate in the fitting surface of the denture with putty rubber base impression material (SPEEDEX, Coltene/Whaledent, Alstalten, Switzerland) and add staple pins to the top surface of the rubber base for mechanical retention with the stone base (Figure 2a).

6. Mount the silicon cast with the attached maxillary denture to the upper member of the articulator and mount the opposing mandibular denture in centric occlusion to the lower member (Figure 2b).

7. Cut a 1-mm groove in the buccal (Figure 3a) and palatal flanges (Figure 3b) parallel to the denture borders and 5 m from the cervical margins of the teeth. The groove perforates the flanges to the fitting surface except at the lateral incisor and first molar areas buccally and midline palatally. Adapt 2-mm-thick vacuum-formed polyethylene sheet (Tray-Vac Complete, Buffalo Dental Manufacturing, Buffalo, NY) over the occlusal and polished surface of the denture and into the groove to form a polyethylene index (Figure 4a). The polyethylene that enters the groove acts as a vertical stopper.

8. Separate the U-shaped segment of the maxillary denture that is bounded by the buccal and palatal grooves and include all artificial teeth (except second molars) and 5 mm of acrylic resin of the denture base facial and palatal to the teeth to make a window. The removed segment represents the contour of the provisional immediate restoration (Figure 4b). Reposition the polyethylene index on the cut denture on the cast to rest on the palatal portion, second molars, and buccal grooves, which act as vertical stops (Figure 4c and d). Verify restorative space for provisional restoration.

9. Place the surgical guide over the silicon cast and drill implant recesses in the silicone cast using the guide and the accompanying surgical kit (In2Guide; Figure 5a). Widen the drilled space in the cast then fill the space with a watery mix of hard stone. Place the surgical guide and then connect each implant analog to the implant mounting tool provided in the digital surgical kit of the implant system. Insert the analogs through the surgical guide and then remove the surgical guide. Attach multiunit abutments (BioHorizons, Birmingham, AL) to implant analogs and thread the titanium caps to the multiunit abutments. Insert the analog with the attached abutments in the implant recesses (Figure 5b). Thread titanium caps to the abutments.

10. Place a prefabricated U-shaped fiber-reinforced composite (FRC) bar (5.5 mm height, Trilor Arch, Bioloren, Italy) over the abutments on the silicon cast for an initial adjustment (Figure 5c). Make 4 holes in the bar opposite to the multiunit abutments and attach the bar to the titanium caps with a composite resin without etching or bonding to facilitate separation of the caps from the bar later. Modify the facial and palatal contour of the bar to follow the contour of the ridge and multiunit abutments by using a carbide bur and a straight handpiece attached to a milling machine (Dentalfarm, Torino, Italy) (Figure 5d).

11. Shorten the bar to the position of the first molar teeth. Modify the bar guided by the transparent polyethylene index until it becomes just fully included in the restorative space (Figure 5e and f). The manufacturer recommended not less than 0.8 mm thickness around each abutment, and distal cantilever extensions should not exceed 10 mm (Figure 5g).²¹ 

12. At the clinical session, insert 4 implants (BioHorizons) in the maxillary ridge of the patient using the mucosal born stereolithographic surgical guide and flapless surgical approach (Figure 6a). Connect the multiunit abutments to the implants using at least 30-Ncm tightening torque.

13. Separate the titanium caps from the bar and thread them to the multiunit abutments in the patient mouth (Figure 6b). Place the modified FRC bar on the patient's mouth over the titanium caps and modify the bar, if necessary, using disclosing media.

14. Cement the FRC bar to the titanium caps in the patient mouth using a dual-polymerizing resin cement (universal resin cement [URC], Bioloren, Saronno VA, Italy) (Figure 6c). Insert the modified denture over the bar to ensure that is no interference. Modify the contour of the bar if necessary. Verify the occlusal relation with opposing teeth (Figure 6d). Remove the bar caps assembly.

15. Sandblast the bar using aluminum dioxide (110 μm at 2 bar pressure) and then clean the surfaces with dry air and ethyl alcohol. Apply silane coupling agent for a few minutes to the bar and caps. Coat the bar and caps with composite bonding material (Visio.Link, Bredent, Senden, Germany).

16. Place rubber dam sheet around multiunit abutments and then screw the FRC bar caps assembly to the multiunit abutments. Place wooden rods in the access screws of the titanium caps to form a channel through the set composite material that allows unscrewing of the provisional restoration. Perforate the polyethylene index to allow passage of the rods.

17. Seat the modified denture in the patient mouth to support the polyethylene index. Insert the polyethylene index over the modified denture to ensure that is no interference between the index and the bar (Figure 6e). Inject dual-curing composite material (Protemp crown, 3M ESPE, Cairo, Egypt) for provisional restorations into the index and beneath the bar intraorally. Seat the polyethylene index carrying the composite resin over the modified denture (Figure 6f), allowing the emergence of wood rods through the preformed holes (Figure 6g). The modified denture supports the polyethylene index at the palatal areas, second molar teeth, and at the buccal groove that acts as vertical stoppers. Ask the patient to close in centric occlusion to ensure intercuspation of the teeth. Complete curing of the composite resin using a light cure device.

18. Remove the polyethylene index and wooden rods after polymerization to clear the formed screw channels (Figure 7a). Unscrew the provisional restoration from the patient's mouth (Figure 7b).

19. Relieve the occlusal surface of the first molar and flatten the occlusal surface of all posterior teeth to avoid occlusal loading on inclined implants. Contour the tissue surface of the prosthesis to facilitate hygiene measures and decrease food debris accumulation.⁵  Finish and polish the provisional prosthesis (Figure 7c).

20. Insert the provisional prosthesis in the patient's mouth and check occlusion with articulating paper. Limit the occlusal contact to the anterior teeth and first premolars only. Finish and polish the provisional restoration. Screw the provisional restoration to multiunit abutments to immediately load the implants on the same day as implant placement⁵  (Figure 7d).

21. Follow-up with patients during the healing period for occlusal adjustments.

22. After osseointegration, convert the provisional restoration to a permanent prosthesis. Unscrew the provisional prosthesis, connect abutment analogs to the metal caps (Figure 8a), and insert the prosthesis in putty rubber base impression material (Figure 8b).

23. Remove the white composite gingival portion and then add pink-colored composite material (Crea. Lign, Bredent) to contour the gingival portion with the aid of the polyethylene index. Restore the occlusal anatomy by adding a tooth-colored composite material to the occlusal surface of posterior teeth using the polyethylene index. Finish and polish the final restoration (Figure 9a).

24. Make any occlusal adjustments in the patient mouth and deliver the final restoration to the patient (Figure 9b).

The fixed prosthesis on 4 implants should be as follows: (1) retaining the screw to be easily retrieved, (2) allowing immediate provisional restoration within 24 hours to 1 week from implant insertion, and (3) permiting ease of adjustments during the healing period. Moreover, the prosthesis should be rigid enough to resist fracture, allow firm splinting to implants, and achieve harmonious occlusion without interference during lateral movements.⁵  The described provisional restoration can be delivered immediately after implant insertion as most of the procedures were performed before surgery, which decreases the number of chairside clinical steps. Moreover, the described technique eliminates the need for making impressions, splinting the impression transfers, and sending impressions to the laboratory, which consumes time and delays the immediate loading to 1 or 2 days after surgery. The chairside procedures reduced the time and costs of laboratory work.

The use of a FRC bar provides rigid reinforcement of the immediate provisional prosthesis, which reduces the incidence of complications such as prosthesis fracture and screw loosening that may affect the implant osseointegration in the critical initial healing period.⁵  Another advantage of the described technique is the achievement of optimum passivity of the provisional restoration, which is crucial for implant success. The passive fit of the restoration eliminates implant micro motions (which may affect the bone/implant interface in the initial healing period)^1,6,7  and reduces technical complications such as chipping or fracture of the veneering material.²²  The passivity is obtained by the direct pickup of the bar to the titanium caps in the patient mouth immediately after implant insertion.

The composite resin material used for the provisional prosthesis provides (1) good color, (2) an esthetically acceptable appearance, and (3) easy occlusal adjustments and modification during the follow-up visits. The chipping or fracture of teeth is easily corrected in the patient mouth without unscrewing the prosthesis and sending it to the laboratory. Unlike conventionally used acrylic resin, the composite resin is not accompanied by heat generation during curing and has no tissue toxicity from the residual monomer.

Although the immediate provisional restoration should have no cantilever extensions posterior to the last implants,⁶  short distal cantilevers of the FRC bar were made to be used in the future for support of cantilever extensions of the definitive prosthesis. The cantilevers did not cause an increase in implant loading because 2 mm of occlusal clearances on the first molar tooth and the cantilever portions of the provisional restoration were made. Drago²³  concluded that short cantilevers not exceeding the mesial/distal lengths of natural first molar tooth did not affect the success of the immediate screw-retained full-arch provisional prosthesis.

Another advantage of the described technique is the adaption, comfort, and satisfaction of the patient with the contour of the provisional restoration due to the duplication of the patient's complete denture Therefore, the provisional restoration provides good lip support, occlusion, vertical dimension, and centric occlusion without making new jaw relations records. The described technique offered easy conversion of the provisional restoration to a permanent one with few modifications that can be done chairside so the patient will not leave the clinic without a restoration. This reduces the cost of temporary and permanent prosthesis compared with conventional methods.

The limitation of the technique includes the several steps performed before the surgical appointment. However, these steps are simple, cost-effective, easy to perform in the dental office without the need for laboratory assistance, able to reduce the length of surgical appointment, and can achieve easy and efficient immediate loading.

The described prosthesis reduces rehabilitation time, minimizes impression problems, and ensures a passive fit of the provisional restoration. The prosthesis provides immediate rehabilitation of 4 implants with ease of adjustment and repair during the entire provisional phase. Moreover, it can be easily converted to the definitive prosthesis with minimal modifications, excellent esthetic results, and reduced costs.