A Novel Method to Pick-up Prefabricated CAD/CAM-Designed Screw-Retained Provisional Prostheses for Immediate Full-Arch Rehabilitations: Liquid Pin Technique

The technique described in this case report, known as the liquid pin technique, addresses the problem of weakening of the prosthesis by the conventional denture conversion process. The technique is not implant system-specific and does not require connections of prosthetic screws. The use of prefabricated CAD/CAM prostheses also bypasses the need for implant position acquisition, thus significantly reducing the treatment and waiting times. Most importantly, this method only requires a few minutes to connect the interim prosthesis to the implants and needs only minimum adjustment.

Clinical Report

An 82-year-old female patient presented with a failing mandibular fixed prosthesis on natural teeth that was mobile and would dislodge upon chewing, causing discomfort and embarrassment. She had six remaining teeth on the mandibular arch from canine to canine holding her existing cantilevered fixed bridge (Figure 1). A panoramic radiograph was taken to evaluate the present situation and assess available bone to accommodate implant placement (Figure 2). Generalized tooth wear was noted with a minor reverse curve of Spee and a reduced vertical dimension. The mandibular retained roots were diagnosed with pulpal necrosis and had a poor prognosis.

Restorative options were presented to the patient, which included extraction of the mandibular dentition followed by delivery of a standard complete denture or an implant fixed prosthesis. The patient indicated she did not want anything that was removable, and therefore a fixed bridge supported by four dental implants was treatment planned.

Presurgical Preparation

The patient's maxillary dentition was scanned with an intraoral scanner (TRIOS 3, 3Shape, 3shape.com). Because of the metal-containing pre-existing restorations in the mandibular arch and a limited number of common landmarks, a new mandibular removable full denture with radiographic markers was fabricated over the patient's remaining roots with the lower fixed bridge removed.¹⁸ The new removable denture was scanned extraorally using the same intraoral scanner. With the patient wearing a radiographic guide, a CBCT scan was performed. The pretreatment digital records obtained for the treatment planning stage were as follows: photographs taken with the patient in relaxed and smile positions; CBCT of the mandibular arch with the mandibular denture with radiographic markers; CBCT of the mandibular denture with radiographic markers extraorally; intraoral scanning of the maxillary dentition; and intraoral scanning of the mandibular denture with radiographic markers.

The digital records from the CBCT and intraoral scanner were merged using a planning software (Blue Sky Plan^®, Blue Sky Bio, blueskybio.com). The implants were planned prosthetically with anterior implants emerging lingual to the incisal edges and posterior implants emerging from the occlusal surfaces of the virtual planned prosthetics. As the new mandibular removable denture was fabricated with stable occlusion, the interim prosthesis was prefabricated based on the occlusal morphologies of the patient's new denture. Bone segmentation was performed within the aforementioned planning software to convert the CBCT rendering of the lower jaw into a surface model.¹⁹ A bone reduction guide and an implant drilling guide were designed using the planning software and a CAD software program (Meshmixer 3.5, Autodesk Inc., autodesk.com) (Figure 3). The guides were subsequently 3D-printed (BLT-A160 3D Metal Printer, Bright Laser Technologies, xa-blt.com) with titanium alloy at a local laboratory.

The provisional prosthesis also was designed using dental CAD software (DentalCAD, exocad, exocad.com) and 3D printed (Sonic Mini 4K 3D Printer, Phrozen, phrozen3d.com) with a nanoceramic hybrid Food and Drug Administration-cleared class II dental resin (OnX, SprintRay, sprintray.com). The provisional prosthesis was then post-cured (Procure 2, SprintRay) according to the manufacturer's instructions. Cylindrical spacers with dimensions of 6.3 mm x 6.3 mm were designed digitally at the tissue surface of the prosthesis for the titanium bases (ti-bases) pick-up.

Implant Surgery

The patient was anesthetized with local anesthetic. A crestal incision was made and a full-thickness mucoperiosteal flap was elevated, exposing the mental nerves. The bone reduction guide with pin connectors was passively fitted onto the alveolar bone and fixated to the mandible with three anchor pins (Guided Pin, Nobel Biocare, nobelbiocare.com) (Figure 4). The retained roots were extracted using forceps and ronguers. Bone reduction was performed with copious saline irrigation using an oval bur (Oval bur, ConMed, conmed.com) until the bone was level with the bone reduction guide to provide sufficient restorative space.^20,21

Following bone reduction, with the bone reduction guide still in place, the implant drilling guide was seated over the pin connectors of the bone reduction guide (Figure 5). The osteotomies were prepared, and four 4.3 mm x 13 mm implants (NobelActive^®, Nobel Biocare) were placed using a fully guided kit (Guided Drill Guide, Nobel Biocare) with good initial stabilities (40 Ncm to 70 Ncm).

Following implant placement, the implant drilling guide was removed from the pin connectors of the bone reduction guide. Two straight anterior and two 17-degree angled transmucosal multi-unit abutments (MUAs) (Nobel Biocare) were inserted and torqued according to the manufacturer's instruction (Figure 6). Custom-made ti-bases that were compatible with the Nobel MUAs were placed on the MUAs, then fastened by prosthetic screws with finger-torque pressure (Figure 7).

Liquid Pin Technique

The interim prosthesis was fabricated with buccal pins to engage the pin connectors on the bone reduction guide (Figure 8). The tissue surface of the prosthesis was relieved 3 mm from the crestal bone in the planning software to allow for soft-tissue thickness after the flap closure. Because the implant and MUA locations were predetermined, a spacer was already created under the prosthesis to pick up the ti-base on top of each MUA (Figure 8).²² With the bone reduction guide still in place intraorally, bite registration material was injected into the relieved areas of the tissue side of the interim prosthesis, which was seated onto the pin connectors intraorally (Figure 9). To accommodate any slight error during implant placement, a fast-setting polyvinyl registration material (Imprint^™ Bite, 3M Oral Care, 3m.com) was used under the interim prosthesis to determine if any interference between the pick-up spacers and the ti-bases existed (Figure 10). Interferences were then marked under the interim prosthesis with a pencil and relieved using an acrylic bur.

Once the ti-bases were ready for pick-up, all four of them were unscrewed. The ti-bases were sandblasted exteriorly, and a universal primer (Monobond Plus^®, Ivoclar, ivoclar.com) was applied onto their outer surfaces. A small-sized rubber dam (15 mm in diameter) was placed around each MUA to prevent the pick-up material from flowing into the undercut areas. Each ti-base was held in place while the liquid pin resin (patent pending) (Dream Smile Dental Ltd, Hong Kong) was injected into each screw hole of the ti-bases, filling the space between the MUA and ti-base, including the MUA's screw channel (Figure 11 and Figure 12). The liquid pin resin was light-cured for 5 to 10 seconds to secure the ti-base temporarily.

To pick-up the ti-bases, each spacer under the interim prosthesis was filled with autopolymerized acrylic pick-up material (LOCATOR CHAIRSIDE^® Attachment Processing Material, Zest Dental Solutions, zestdent.com). The interim prosthesis was then seated back onto the pin connectors while the pick-up material was being dispersed around the ti-bases and allowed to set. Once the material was fully hardened, the prosthesis was removed by finger pressure. Upon removal of the interim prosthesis intraorally, the ti-bases were fixated inside it (Figure 13). Any residual resin inside the screw channels of the MUAs and beneath each ti-base could be easily removed using a small excavator and an endodontic file.

Delivery of the Interim Prosthesis

With this procedure, following pick-up of the ti-bases, screw channels need to be created through them so the interim prosthesis can be screw-retained. The screw channels were created using two drills that are included in the liquid pin package. The first drill, which has a smaller diameter than the other drill, was used from the base of the ti-base to create a small opening toward the occlusal side of the prosthesis (Figure 14). The second, larger-diameter drill was used to enlarge the screw-access hole from the occlusal side of the prosthesis down to the top of the ti-base following the hole created by the smaller drill that was utilized from the tissue side of the ti-bases (Figure 15). This step ensures complete seating of the prosthetic screw and is repeated at each of the four screw channels.

The bone reduction guide was removed intraorally after picking up the ti-bases. The soft-tissue flap was closed using continuous 4-0 Vicryl sutures (Ethicon, ethicon.com). The connecting pin arms of the interim prosthesis were cut off and polished. The prosthesis was seated back onto the MUAs, and the prosthetic screws were torqued to 15 Ncm according to the manufacturer's recommendation (Figure 16). The screw-access holes were sealed with Teflon tape and temporary composite material (Telio^® CS Inlay, Ivoclar) (Figure 17). Occlusion was checked and minimal adjustments were made (Figure 18). A postoperative panoramic radiograph was taken to document implant placement and seating of the interim prosthesis (Figure 19).

Delivery of the Definitive Prosthesis

After osseointegration and soft-tissue healing the interim prosthesis was removed intraorally revealing healthy soft tissue without evidence of inflammation (Figure 20). Scan bodies were placed on the implants and intraoral scanning (TRIOS 3) was performed to record both the positions of the scan bodies and the soft tissue of the lower arch (Figure 21). The scan bodies were then removed intraorally and photogrammetry dominos (iCam 4D, Voxel Dental, voxeldental.com) were connected to the MUAs for the capturing of the implants' positions extraorally (Figure 22). The intraoral scanning and photogrammetry digital data were merged into the proprietary software and exported to the CAD software (exocad) to design a full-arch implant-supported fixed prosthesis (Figure 23). The design would forgo ti-bases and utilize Rosen screws (Rosen Implant Solutions, rosen-implant-solutions.com) to directly connect the prosthesis to the MUAs, increasing prosthetic thickness at those connections. The definitive prosthesis was milled from a zirconia block (BSM Aconia^® SHT-ML 98x25mm, Besmile Dental America, bsmdental.com) on a milling unit (XMill 500 Plus, XTCera, en.xtcera.com).

The definitive full-zirconia restoration was inserted and fixed to the MUAs with Rosen screws with a torque of 25 Ncm, per the manufacturer's recommendations. The occlusion, esthetics, and phonetics were evaluated (Figure 24). An occlusal view of the definitive prosthesis showing the screw-access holes in relation to the prosthetic teeth and minimal cantilever bilaterally demonstrated the fit within the recommended anterior-posterior ratio (Figure 25).²³ The screw-access holes were sealed with Teflon tape and temporary composite material (Telio CS Inlay). The passivity and fit were confirmed radiographically (Figure 26). The definitive monolithic zirconia prosthesis provided a pleasing functional and esthetic outcome with which the patient was highly satisfied. She was followed-up at 3 and 6 months post-prosthesis delivery; her homecare demonstrated good maintenance of the reconstruction.

Discussion

All-on-4 implant procedures have become a prevalent means for replacing missing teeth on an edentulous arch since the introduction of this protocol by Dr. Paulo Malo in the 1990s.²⁴ Since then, interim prostheses typically have been delivered the same day or within 48 hours following surgical implant placement. Usually, for prostheses delivered the same day, clinicians convert the patient's existing denture for screw retention by hollowing the denture to create large pick-up holes around the titanium cylinders placed on the MUAs, which are picked-up with acrylic resin. The denture flange is then cut, and acrylic added and removed at the intaglio surface to create a convex surface for hygienic purposes. This "denture conversion" process, however, can potentially contaminate the surgical site and is quite labor-intensive.²⁵

CAD/CAM technology has revolutionized full-arch rehabilitation with implants.^26-29 With advanced 3D planning, clinicians can perform teeth extraction, bone reduction, guided implant placement, and MUA connection to a prefabricated provisional for immediate loading in a predictable manner.³⁰ However, it is still common for clinicians to use the large pick-up holes to connect the temporary titanium cylinders, which can weaken the structure of the prosthesis (Figure 27).³¹ One method to streamline the workflow has involved the development of a MUA coping fastened with a special screw (ie, a PEEK screwhead that can be forcibly removed from the bottom fastener headless screw).³² However, in this system, the retention force was found to be very high as the number of implants to be picked up increased. It is also system specific and only works on certain types of MUAs.

The liquid pin technique simplifies the pick-up procedure in a fast and accurate manner. Additionally, only a minimal amount of prosthesis resin is removed in order to fit over the temporary cylinders, thus enabling a stronger interim prosthesis. The biomaterials used comprise hydroxyethyl methacrylate, silicon dioxide, and urethane dimethacrylate, which is light-curable. The technique is named as such because of the rheological and viscoelastic properties before and after setting. Before consolidation, the ease of flow allows the material to enter the small and delicate spaces between the ti-base and MUA, including the screw channel. After complete setting, the prosthesis is firm but flexible. Therefore, it is strong enough to avoid the displacements of ti-bases during the relining, yet easily removable afterwards.

This novel technique could be applied in various implant systems and is not implant brand specific. The operator can use the ti-bases and prosthetic screws that came from either the same or a compatible implant system. Preparations of large channels are no longer required in the prosthesis during the pick-up procedure. Only a spacer to accommodate the size of the ti-base is needed to connect the prosthesis.

There are several advantages to using the liquid pin technique with CAD/CAM technology to connect the interim prosthesis to the MUAs. First, minimal material is removed from the prosthesis prior to pick-up. No unnecessary material is removed compared to a conventional technique, especially when the temporary cylinders are divergent. This significantly enhances the strength of the interim prosthesis. Second, no additional implant parts other than the ti-bases are required, simplifying the prosthesis pick-up procedure. Third, treatment cost and time is minimized due to the simplicity of the technique, which requires minimal training. Chairside time is also reduced. Fourth, fabrication of a one-piece CAD/CAM provisional together with ti-base pick-up greatly reduces the risk of prosthetic fracture. Lastly, the technique bypasses many technical difficulties in digital implantology when the prosthetic designer is not readily available. It omits the need to capture implant positions, design and manufacture the provisional prosthesis, and post-processing after implant surgery.

A limitation of this technique, however, is that the low profile of the ti-base may not allow for enough surface area for the pick-up material to adhere to the base of the prosthesis. This can be a particular problem if the MUA platform is subgingival. To overcome this problem, a MUA with a taller gingival height may be selected to raise the prosthetic platform equal- or supragingivally. The height of the ti-base can also be increased by prebonding some pick-up material. Furthermore, a temporary cylinder of reduced height can also be used for a more secure connection to the base of the prosthesis.

A provisional prosthesis stabilized on a bone-borne surgical guide facilitates the relining process since the area between the spacers and the MUAs can be more easily controlled without over-adjustment, and the interference is more easily identified. Using a minimal amount of acrylic resin could also avoid major ti-base displacements. Nevertheless, fabricating a bone reduction guide with a stackable surgical template and a fixed temporary denture requires advanced skills in digital planning.

Moreover, the liquid pin technique can also be used in a conventional "denture conversion" technique. The liquid pin protocol is similar to the direct, chairside pick-up of the overdenture, with which many general dentists and assistants are familiar. The pick-up of the prefabricated prosthesis requires only a few minutes, and the prosthesis can be delivered shortly after dental implant placement.

Conclusion

The liquid pin technique improves the digital workflow by accelerating efficiency and aids the immediate loading protocol by providing a strong and rigid temporary prosthesis on the day of surgery. This helps eliminate additional visits to insert the interim prosthesis and facilitates patient management. Further research is required to validate the long-term success of this digital protocol using the liquid pin technique.

Disclosure

Dr. Ma is the developer of Liquid Pin. All other authors had no conflicts of interest to report.

About the Authors

Andrew Ma, DDS, DMSc
Part-time Clinical Lecturer, Restorative Dental Sciences, Faculty of Dentistry, The University of Hong Kong, Hong Kong, China; Private Practice, Hong Kong, China

Brian Chan, BDS, MSc
Private Practice, Hong Kong, China

Ian Yip, BDS, MDS
Private Practice, Hong Kong, China

Chung Kwai Hung, BDS, MSc
Private Practice, Hong Kong, China

Gregori M. Kurtzman, DDS, MAGD
Former Assistant Clinical Professor, University of Maryland School of Dentistry, Baltimore, Maryland; Private Practice, Silver Spring, Maryland; Diplomate, International Congress of Oral Implantologists

Dennis P. Tarnow, DDS
Clinical Professor and Director of Implant Education, Columbia University College of Dental Medicine, New York, New York

References

1. Magrin GL, Rafael SNF, Passoni BB, et al. Clinical and tomographic comparison of dental implants placed by guided virtual surgery versus conventional technique: a split-mouth randomized clinical trial. J Clin Periodontol. 2020;47(1):120-128.

2. Oberoi G, Nitsch S, Edelmayer M, et al. 3D printing-encompassing the facets of dentistry. Front Bioeng Biotechnol. 2018;6:172.

3. Whitley D 3rd, Eidson RS, Rudek I, Bencharit S. In-office fabrication of dental implant surgical guides using desktop stereolithographic printing and implant treatment planning software: a clinical report. J Prosthet Dent.2017;118(3):256-263.

4. Revilla-Leon M, Rubenstein J, Methani MM, et al. Trueness and precision of complete-arch photogrammetry implant scanning assessed with a coordinate-measuring machine. J Prosthet Dent. 2023;129(1):160-165.

5. Tohme H, Lawand G, Chmielewska M, Makhzoume J. Comparison between stereophotogrammetric, digital, and conventional impression techniques in implant-supported fixed complete arch prostheses: an in vitro study. J Prosthet Dent. 2023;129(2):354-362.

6. Papaspyridakos P, Vazouras K, Chen YW, et al. Digital vs conventional implant impressions: a systematic review and meta-analysis. J Prosthodont. 2020;29(8):660-678.

7. Chochlidakis K, Papaspyridakos P, Tsigarida A, et al. Digital versus conventional full-arch implant impressions: a prospective study on 16 edentulous maxillae. J Prosthodont. 2020;29(4):281-286.

8. Rojas Vizcaya F. Retrospective 2- to 7-year follow-up study of 20 double full-arch implant-supported monolithic zirconia fixed prostheses: measurements and recommendations for optimal design. J Prosthodont. 2018;27(6):501-508.

9. Papaspyridakos P, Chochlidakis K, Kang K, et al. Digital workflow for implant rehabilitation with double full-arch monolithic zirconia prostheses. J Prosthodont. 2020;29(6):460-465.

10. Papaspyridakos P, Chen YW, Gonzalez-Gusmao I, Att W. Complete digital workflow in prosthesis prototype fabrication for complete-arch implant rehabilitation: a technique. J Prosthet Dent. 2019;122(3):189-192.

11. Alp G, Murat S, Yilmaz B. Comparison of flexural strength of different CAD/CAM PMMA-based polymers. J Prosthodont.2019;28(2):e491-e495.

12. Bidra AS, Tischler M, Patch C. Survival of 2039 complete arch fixed implant-supported zirconia prostheses: a retrospective study. J Prosthet Dent. 2018;119(2):220-224.

13. Tischler M, Patch C, Bidra AS. Rehabilitation of edentulous jaws with zirconia complete-arch fixed implant-supported prostheses: an up to 4-year retrospective clinical study. J Prosthet Dent.2018;120(2):204-209.

14. Gonzalez J, Triplett RG. Complications and clinical considerations of the implant-retained zirconia complete-arch prosthesis with various opposing dentitions. Int J Oral Maxillofac Implants. 2017;32(4):864-869.

15. Papaspyridakos P, Rajput N, Kudara Y, Weber HP. Digital workflow for fixed implant rehabilitation of an extremely atrophic edentulous mandible in three appointments. J Esthet Restor Dent.2017;29(3):178-188.

16. Kammeyer G, Proussaefs P, Lozada J. Conversion of a complete denture to a provisional implant-supported, screw-retained fixed prosthesis for immediate loading of a completely edentulous arch. J Prosthet Dent.2002;87(5):473-476.

17. Misch CM. Immediate loading of definitive implants in the edentulous mandible using a fixed provisional prosthesis: the denture conversion technique. J Oral Maxillofac Surg.2004;62(9 suppl 2):106-115.

18. Scherer MD, Roh HK. Radiopaque dental impression method for radiographic interpretation, digital alignment, and surgical guide fabrication for dental implant placement. J Prosthet Dent. 2015;113(4):343-346.

19. Wang L, Chen KC, Gao Y, et al. Automated bone segmentation from dental CBCT images using patch-based sparse representation and convex optimization. Med Phys. 2014;41(4):043503.

20. Balshi TJ, Wolfinger GJ, Slauch RW, Balshi SF. A retrospective analysis of 800 Branemark System implants following the All-on-Four^™ protocol. J Prosthodont. 2014;23(2):83-88.

21. Malo P, de Araujo Nobre M, Lopes A, et al. All-on-4^® treatment concept for the rehabilitation of the completely edentulous mandible: a 7-year clinical and 5-year radiographic retrospective case series with risk assessment for implant failure and marginal bone level. Clin Implant Dent Relat Res. 2015;17 suppl 2:e531-e541.

22. Wu YL, Wu AY. A method of fabricating an accurate repositioning device for relocating multiple multiunit abutments. J Prosthet Dent. 2017;118(4):564-566.

23. Drago C. Cantilever lengths and anterior-posterior spreads of interim, acrylic resin, full-arch screw-retained prostheses and their relationship to prosthetic complications. J Prosthodont. 2017;26(6):502-507.

24. Malo P, Rangert B, Nobre M. All-on-4 immediate-function concept with Brånemark System implants for completely edentulous maxillae: a 1-year retrospective clinical study. Clin Implant Dent Relat Res. 2005;7 suppl 1:S88-S94.

25. Nulty A. A literature review on prosthetically designed guided implant placement and the factors influencing dental implant success. Br Dent J. 2024;236(3):169-180.

26. Verstreken K, Van Cleynenbreugel J, Marchal G, et al. Computer-assisted planning of oral implant surgery: a three-dimensional approach. Int J Oral Maxillofac Implants. 1996;11(6):806-810.

27. Harris BT, Montero D, Grant GT, et al. Creation of a 3-dimensional virtual dental patient for computer-guided surgery and CAD-CAM interim complete removable and fixed dental prostheses: a clinical report. J Prosthet Dent. 2017;117(2):197-204.

28. Pozzi A, Gargari M, Barlattani A. CAD/CAM technologies in the surgical and prosthetic treatment of the edentulous patient with biomymetic individualized approach. Oral Implantol (Rome). 2008;1(1):2-14.

29. Chochlidakis KM, Papaspyridakos P, Geminiani A, et al. Digital versus conventional impressions for fixed prosthodontics: a systematic review and meta-analysis. J Prosthet Dent. 2016;116(2):184-190.e12.

30. Orentlicher G, Abboud M. Guided surgery for implant therapy. Oral Maxillofac Surg Clin North Am.2011;23(2):239-256, v-vi.

31. Marchack CB. CAD/CAM-guided implant surgery and fabrication of an immediately loaded prosthesis for a partially edentulous patient. J Prosthet Dent. 2007;97(6):389-394.

32. Kofford B, Drago C, Nejat AH, Elshewy M. A novel approach for converting a mandibular complete denture to a fixed interim, screw-retained implant prostheses: a case report. J Prosthodont. 2021;30(1):13-18.