Prosthetically Driven Computer-Guided Implant Placement and Restoration Using CEREC: A Case Report

One of the most common reasons for patient visits to a dental clinic is for esthetic and/or functional replacement of missing teeth.¹ Traditionally, when replacing a single missing tooth, dentists have focused on implant surgery guided by currently existing bone, without giving much consideration to the restorative design and esthetics of the final restoration.

With the introduction of successful bone grafting materials and incorporation of cone-beam computed tomography (CBCT) and computer-aided design/computer-aided manufacturing (CAD/CAM) technology, however, new advancements in the understanding and implementation of implant dentistry have occurred.^2,3 More specifically, use of these technological advancements in a pre-doctoral clinical setting allows for students and faculty to work together and design intraoral surgical guide templates to place dental implants. From a surgical perspective, use of digital technology to perform computer-guided surgery can optimize hard- and soft-tissue healing and streamline treatment.^4,5

Sufficient preoperative planning combined with a CAD/CAM-milled surgical template enables the placement of implants with minimal invasion and fewer complications.^3,5,6 Esthetic and functional advancements have also been achieved in biomaterials with the introduction of polymer-infiltrated-ceramic-network (PICN) materials. Ceramic matrix materials such as ENAMIC^® (VITA, vita-zahnfabrik.com), an interpenetrating phase ceramic matrix material, have demonstrated improvements such as more closely imitating natural dentition and improved fracture resistance.^7,8 The copolymer's structure is highly resistant to strength degradation and reduces stress transmission to the implant, thereby maximizing the esthetics and longevity of the final restoration.⁷

Utilizing digital technology can improve the patient's experience and minimize potential discrepancies.^9,10 This novel approach has streamlined clinical education at the Boston University School of Dental Medicine while providing the school's patient population with exemplary care.

In this case report the patient had a minimal amount of keratinized mucosa present prior to implant surgery, and a two-stage implant protocol was used. Esfahanizadeh et al showed that there is association between width of keratinized mucosa and peri-implant soft-tissue health and demonstrated that at least 2 mm of peri-implant keratinized mucosa is recommended.¹¹ In addition, the presence of a keratinized tissue border at the peri-implant tissue assists in development of close tissue adaptation and marginal seal at the implant surface, which facilitates attachment of connective tissue fibers that resist mechanical stress.¹²

In presenting this case report the authors intend to: (1) emphasize the predictability and efficiency of restoratively driven computer-guided implant dentistry, (2) describe how a polymethyl methacrylate (PMMA) CEREC^® Guide 2.0 surgical guide (Dentsply Sirona, dentsplysirona.com) was designed and used intraorally for implant placement in a pre-doctoral clinical setting, (3) underscore the smooth clinical workflow following implant placement with implant uncovering and restoration in a single visit, and (4) highlight the esthetic and functional results of the VITA ENAMIC^® IS block.

A 69-year-old healthy man presented to the authors' student clinic for a single implant placement in an edentulous area of the lower right mandibular first molar. The tooth had been extracted at an outside clinic 4 months prior and a bone graft placed in the socket. A CBCT scan using the GALILEOS^® system (Dentsply Sirona) was obtained, and a polyvinyl siloxane impression of the edentulous and opposing arch was taken as part of the workflow protocol developed in the clinic.

Optical impressions of the models were taken using the CEREC AC Bluecam. A crown was designed using the CEREC software (virtual wax-up) for tooth No. 30 according to the patient's prosthetic needs, and this was exported for use in the GALILEOS software (Figure 1). After verification of the integrated information into GALILEOS, an implant was selected based on anatomical landmarks and the design of the future restoration (Figure 2 and Figure 3).

Virtual placement of the selected implant was performed to verify the chosen dimensions (Figure 4 and Figure 5). This data was exported into the CEREC software for design of a PMMA CEREC Guide 2.0 surgical guide (Figure 6) followed by machining using an MC XL mill (Dentsply Sirona) (Figure 7). The proper seating of the guide was verified intraorally prior to surgery (Figure 8 and Figure 9).

The surgical procedure took place in the school's Oral Surgery Department and involved local anesthesia with two carpules of lidocaine 2% with epinephrine 1:100,000 administrated via inferior alveolar nerve block and local infiltration. A full-thickness mucoperiostal flap with mesial and distal sulcular incision was performed to maximize retained keratinized tissue surrounding the implant. A NobelReplace^® Tapered 5-mm x 11.5-mm implant (Nobel Biocare, nobelbiocare.com) was placed using the CEREC Guide 2.0 and the "L" size Sirona drill key system. A two-stage implant surgery protocol was chosen for this case; therefore, a cover screw was placed followed by 3-0 chromic gut sutures (Figure 10 and Figure 11).

The patient presented 3 months after implant placement for stage-two uncovering of the implant with same-day delivery of the final restoration. This approach allows for the creation of a better emergence profile and an improved esthetic result.¹³ A crestal incision was performed to uncover the implant. A digital impression of the implant position was taken with a ScanPost (Dentsply Sirona) using the CEREC AC Omnicam. The final restoration was designed with the CEREC software to machine a restoration using a VITA ENAMIC IS block shade 2M, with the MC XL mill (Figure 12 through Figure 15).

The crown was tried-in intraorally and a bitewing radiograph was taken to verify proper seating of the various implant restoration components. The final ENAMIC restoration was polished according to the manufacturer's recommendation and cemented to the TiBase (Dentsply Sirona) using Multilink^® Hybrid Abutment Cement (Ivoclar Vivadent, ivoclarvivadent.com). Finally, 3-0 chromic gut sutures were placed and the patient was discharged (Figure 16 through Figure 18).

Implementation of 3D diagnostic technology and CAD/CAM-guided surgery streamlines clinical workflow.¹⁴ It facilitates collaboration between different departments of the dental school, thereby expediting edification and optimizing advanced, secure, restoratively driven treatment for patients.

In the United States, general dentists are increasingly placing and restoring dental implants and soon may become the principle provider of single implant placement. In a randomized controlled study Younes et al showed that freehand implant surgery demonstrated low accuracy in 3D position as compared to fully guided surgery. When precise implant placement position is indicated, guided surgery should be considered the gold standard.¹⁵ Pozzi et al showed in a review that computer-guided implant surgery may have additional costs, which clinicians should evaluate when considering cost-effectiveness, but also take into account the reduction in chairtime, potential decrease in postoperative pain and swelling, and potential increase in accuracy.¹⁶

The material of choice used for the final restoration plays an important role in the longevity of the restoration. In this clinical case the authors used ENAMIC, which is an interpenetrating phase ceramic matrix material designed to improve resistance to fracture and decrease stress transmitted to the implant. The interconnected network of ceramic and polymer creates a structure that provides a "backbone" to ensure adequate stiffness but is also resistant to crack propagation due to the polymer network. It is important to understand that both ceramic and polymer networks are connected within themselves. If either of these two networks were removed individually a physical structure would still remain, ie, a porous block. This is very different than a conventional composite resin that has individual particles surrounded by a resin matrix. If the entire resin component was to be removed, there would simply be a ceramic/glass powder remaining. This PICN material class still has low modulus values that may create a restoration that is too flexible under stress.^8,17

Analysis of material properties demonstrates the correlation between modulus values and the ceramic network. In a study by He and Swain,¹⁷ a modulus value of about 30 GPa and fracture toughness of 1.72 MPa.m^1/2 was found for ENAMIC. The material has a similar response to stress as tooth enamel, and its high fracture toughness is due to a crack deflection mechanism related to the interconnected structure.¹⁸

Resistance to damage under stress is particularly important for implant-based restorative materials, as loads placed on the implants by the patient can be several times higher than normal biting force due to lack of proprioception. A study by Coldea examined damage tolerance of a variety of materials, including glass-ceramics, porcelain, zirconia, and ENAMIC, with the latter demonstrating the highest resistance to indentation damage and showing more damage tolerance than commonly used dental ceramics.⁸

A digital workflow system and restoratively driven approach were used to prosthetically plan and place an implant in the site of a lower right mandibular first molar after tooth extraction and grafting. Preoperative planning incorporated CBCT to design and mill a stable, tooth-supported surgical guide, followed by implant placement and subsequent osseointegration. Implant uncovering and restoration of the implant were performed chairside in a single visit. TiBase and ENAMIC IS block were used to produce an esthetically pleasing, clinically outstanding screw-retained implant crown.

David Dano, DMD
Clinical Assistant Professor, Department of General Dentistry, Boston University Henry M. Goldman School of Dental Medicine, Boston, Massachusetts

Monica Stiteler, DMD
Advanced Education in General Dentistry (AEGD) Resident, Tufts University School of Dental Medicine, Boston, Massachusetts

Russell Giordano, DMS, DMSc
Associate Professor, Department of Restorative Sciences & Biomaterials, Boston University Henry M. Goldman School of Dental Medicine, Boston, Massachusetts