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Inside Dentistry
June 2020
Volume 16, Issue 6

Down to a Science

Virtual planning and guided surgical options improve the predictability of implant outcomes

Sefira Fialkoff

More than 50 years ago, the first osseointegrated implants were used to replace missing teeth.1 Nowadays, implant therapy is one of the most sought after treatment options for individuals who require oral rehabilitation and for those who wish to improve their esthetics or recover masticatory capacity.2 There has been a growing consensus within dentistry that procedures should be kept as minimally invasive as possible. Through its constant evolution, the field of implant dentistry has seen a decrease in average surgical times, a decrease in associated morbidity, and an increase in safety regarding the surgical process. When implemented, digital planning and guided surgery provide valuable information and permit stringent backward planning to optimize the implant position and prosthetic result, thus improving the safety and efficiency of the surgical procedure and rendering the restorative outcome more predictable in terms of function, biology, and esthetics.3

Restoration-Driven Treatment Planning

The terms immediate, recent, delayed, and mature have been used in the literature to describe the timing of implant placement in relation to the time of extraction, soft-tissue healing, and guided bone regeneration procedures.4 Although there is no universally agreed upon time frame for each category, the literature suggests that an immediately placed implant is one that is placed within the first 1 to 10 days and a delayed implant is one that is placed within 6 to 10 weeks.5-9

"My decision regarding when to place an implant is based on the gingival phenotype as well as the availability of palatal/lingual bone," explains Nicolas Ravon, DDS, MSD, a periodontist in Beverly Hills, California. "If the phenotype is thick, the patient presents with no gingival display on smiling, and there is an adequate amount of palatal bone, I will proceed with immediate implant placement and provisionalization. If the biotype is thin, there is significant gingival display with a high smile line, and little palatal bone to engage, I will choose a delayed immediate approach."  Implants placed into fresh extraction sockets have a high rate of survival, ranging between 93.9% and 100%10; however, immediate implantation in the posterior region of the mandible has a better prognosis than in the posterior region of the maxilla.11Successful osseointegration and complete bone healing can be observed among patients in whom implants were placed immediately after tooth extraction without incision.12 As an alternative to immediate implant placement, delayed placement offers several advantages, including the resolution of any infection at the site and an increase in the area and volume of soft tissue for flap adaptation. Unfortunately, these advantages can be diminished by concomitant ridge resorption in the buccolingual direction and increased requirements for tissue augmentation.13

Osseointegration is an indication of a favorable response of the surrounding bone to the insertion of a dental implant and a key indicator that an implant has been placed successfully. The success of a dental implant is dependent on many factors, such as bone quantity and quality, surgical and prosthetic techniques, prosthetic design, and the nature of the functional load that is applied to it.14 These factors also help to determine which materials will be best to use.

"It used to be that implants were only placed where there was enough bone to support them, but now we have to do what I call restoration-driven implant placement," explains Jeff Lineberry, DDS, a cosmetic dentist in Mooresville, North Carolina. "We need to design the final restoration and know where we want to put it first, then we can decide if the bone that's present will or will not support the final restoration and work from there." By considering the individual characteristics of the patient and indication, one can develop a personalized plan for a patient's dental implants. "Start with the end result," concurs Ken Hovden, DDS, a cosmetic dentist in Daly City, California, "then work backwards to where you are today. That will guide your treatment planning." A systematic approach to diagnosis and treatment planning is fundamental to the success of dental implants and their long-term functionality.

Digital planning can help clinicians simplify their procedures from implant placement to the realization of the final prosthetic restoration. In a digital workflow, technology plays a significant role in every step of the implant treatment process, including the use of digital intraoral impressions, cone-beam computed tomography (CBCT) scans, digital wax-ups, implant planning software, and 3D-printed surgical guides.15-17

The evaluation of 3D CBCT and optical scan data within modern implant planning software can facilitate carefully simulated surgical and prosthetic phases. Implants and abutments can then be "virtually" planned based on bone volume and quality, the location of anatomical structures, and prosthetic and esthetic evaluations. This 3D planning also allows for the presurgical determination of prosthesis path of insertion, screw chamber locations, componentry space, and abutment choices as well as the presurgical fabrication of individual abutments. Considered by many to be the standard of care, 3D planning has been shown to enable clinically sound esthetic results.18-20

Surgical Guidance

When compared with free-hand surgery, guided surgery using computer-generated, stereolithographic surgical templates significantly reduces the chance for a positional error at the time of implant placement.21,22 This technique offers many significant benefits over traditional freehand procedures, particularly the ability to precisely translate the treatment plan directly to the surgical field.23-25 However, the protocol of static surgical guidance involves multiple steps during which error can still potentially be introduced, from data collection and planning to surgical template fabrication and placement of the implants.26

With dynamic navigation, a type of freehand surgery in which the handpiece is guided relative to the patient position by motion-tracking, implant surgeons can evaluate a patient, scan the patient, plan the implant position, and perform the implant surgeryall in the same day without the delay or cost associated with fabricating a static surgical guide.27 "This is the future," says Ravon. "It's the same concept as in neurosurgery."

A dynamic navigation workflow requires a CBCT scan with fiducial data, virtual implant planning, calibration, and implant placement in accordance with the 3D image on the navigation screen.27 "The problem with stereolithographic surgical guides is that there's no representation of the tooth position in space," explains George A. Mandelaris, DDS, MS, a periodontist in Chicago, Illinois. "Dynamic navigation is like a GPS that provides a targeted view of the surgical plan in relation to the patient and the drill tip, allowing us to know exactly where we are in all planes of space throughout the operation. You are able to perform the surgery while targeting the optimal final tooth position in real time."

The benefits of dynamically guided surgery include real-time feedback, a streamlined digital workflow, improved surgical visualization, and adaptability to intraoperative findings.28 Despite these benefits, dynamic navigation is not ideal for every indication. "Right now, the navigation surgery workflows for full arch immediate load therapy are still in the development phase," continues Mandelaris, "but this technology is constantly advancing, and a predictable solution for the maxillary and mandibular arches will soon emerge and allow for more minimally invasive surgery to take place."

Materials for Implants and Implant Restorations

A sound knowledge of dental implants’ restorative capabilities and a thorough understanding of patients’ individual indications can go a long way toward preventing implant failures.29,30 The selection of a restorative material is an important decision because it could have an influence on cases involving excessive biting force or parafunctional habits, as well as protect the bone from sustaining load-bearing damage. Regarding the implant itself, an ideal material should be biocompatible and strong as well as provide adequate resistance to corrosion, wear, and fracture.31,32 Similarly, an ideal implant retention mechanism should consider the patient, the intraoral conditions of the indication, and the benefits and limitations of the current options available.

“When choosing materials and design, say for a single implant, I start by looking at where in the arch the indication is,” explains Lineberry, “I also need to factor in the patient’s needs in terms of wear and tear and esthetics.” There are a variety of dental implant materials available. Titanium is the most popular metal used to support removable and fixed prostheses due to its mechanical strength, biocompatibility, and long history of use.33,34 More recently, zirconium, often offered as a one-piece implant/abutment design, has been used as a more esthetic alternative.35 However, despite zirconia's excellent biocompatibility and tissue integration, as well as its low affinity to plaque and favorable biomechanical properties, early failures have been shown to be higher among zirconia implants than titanium implants.35 Polymeric materials, such as polyetheretherketone, are also being studied for potential uses in clinical implant dentistry.

Their physical and mechanical properties are close to those of bone.36 In addition to the primary material used, there are a number of possible surface modifications that can be made to improve the biocompatibility of implants and impart antimicrobial properties. Implants may be modified with plasma spraying, ion dispersion, and coatings of bioactive materials and antimicrobial proteins/peptides.37-40 Choosing the optimal material for implant applications is a major factor in the clinical success of implant-retained restorations. Regarding the restoration of implants, there are advantages and limitations associated with both cement retention and screw retention. Cementation is more common, and its advantages include the ability to compensate for improperly inclined implants, easier achievement of a passive fit due to the cement layer between the abutment and restoration, and lack of a screw access hole, which allows for an intact occlusal table and easier control of occlusion. However, it can be difficult to completely remove excess cement, and retained cement is associated with the development of peri-implant mucositis and peri-implantitis.41,42 Screw retention makes it easier to remove restorations for hygiene maintenance, repairs, or surgical interventions. With the introduction of angulated screw channel solutions, screw-retained restorations have become available for a wide range of indications.

As technology and material development have continued to advance, there has been a direct impact on implant dentistry and the success of implants. “The implants of today are dramatically better than those of 20 years ago,” says Hovden, “I’m in no rush to place an implant in a young patient when I don’t have to because perhaps there will be something even better available within the next few years. For now, if I can do something more conservative, I will.” James J. Wu, DDS, an implantologist from Tewksbury, Massachusetts agrees, “The longest study we have looking at the success rate of a dental implant replacement tooth is about 25 years. That success rate is not 100% either. How do we then counsel the 30-year-old who needs to have a tooth replaced?”

Materials and methods continue to advance as patient demand for implants grows. “Just like any other new technology, you have to be steadfast and fastidious about learning in order to master it,” says Mandelaris. Although doctors may choose to not immediately incorporate a new technology or material into their practice, they should nonetheless remain knowledgeable about any advancements in order to ensure the best service and results for each patient.

The Next Evolution

Imaging technology has precipitated a paradigm shift in implant dentistry. The role of CBCT and optical scanning in presurgical diagnosis and treatment planning will likely continue to grow. As implant dentistry evolves, dentists who provide implant therapy must determine how and when to adopt technologic innovations and integrate them into their workflows with the understanding that a more comprehensive knowledge of the techniques and products available will better enable them to provide the most optimal treatment for their patients' individualized needs.

References

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