Reaching Initial Stability
Important considerations as implant therapy threads its way into general practice
In a 2020 Inside Dentistry survey, 69% of responding general dentists said that they placed implants. As technology and materials continue to evolve, that number could become even larger; however, the need for a strong understanding of the field of implant dentistry will remain paramount for anyone who wishes to enter this space. Knowing this, Inside Dentistry's 2021 Implant Issue guest editor, Bobby Birdi, DMD, MSc, selected four important aspects of implant dentistry to explore in this article: implant selection, full-arch therapy, digital workflow, and guided surgery/robotics.
"These topics highlight the breadth of the different aspects of implant dentistry that we are seeing today," Birdi says. "More and more clinicians beyond specialists are venturing into this field and doing more and more implant therapy. The implant companies continue to develop new components and workflows. Addressing these new developments is important."
One of the most critical decisions that a dentist makes early on in the process of implant treatment is the selection of the implant itself. "We are seeing more different types of implants being made, which feature different thread patterns and connections," Birdi says. "It can be difficult for clinicians to sort through, especially because many of these innovations do not have much evidence behind them yet."
The diameter of an implant and its connection are key considerations. "The current thought process is to have the diameter of the connection smaller than that of the implant, which is also known as platform switching or platform shifting," says Joseph Kan, DDS, MS, a professor at the Loma Linda University School of dentistry who maintains a private practice limited to prosthodontics and implant surgery in Covina, California. "Theoretically, that moves the gap of the connection inward and away from the bone. Some believe that will minimize bone loss around the implant."
Using an implant system with one connection diameter for all of its implant sizes can sometimes make sense because it makes selecting components easier.
However, Kan notes that this could cause implants with a larger diameter to have a weaker connection. "In addition," he says, "because larger-diameter implants are typically used for bigger teeth, such as molars, if the connection remains smaller, the emergence profile will be much more abrupt. Some believe that the emergence angle becomes exaggerated, which can increase the risk of peri-implantitis."
According to Kan, generally, smaller-diameter implants permit better esthetics and, as a result, are preferable in the anterior region, whereas larger-diameter implants are more appropriate in the posterior region for functional purposes. The length of the implant, meanwhile, may not matter beyond 8 mm to 10 mm. "Based on studies and research, most of the load or stress will be at the coronal portion of the implant," he says.
The design of an implant's threading and its connection type are interesting considerations but may have less impact on the success of a case. "It does not hurt to aggressively thread," Kan says. "I find it helpful in certain situations, such as immediate loading, especially in the esthetic zone. It makes me feel a bit more confident, but regarding the research that has been conducted, it does not seem to make a significant difference. Similarly, different implant connection types can provide more stable connections and better seals in certain situations, but thousands of implants have been placed with older connections over the past few decades, and they are not failing."
In many cases, price might not matter much either. "Implant designs today are fairly universal," Kan explains. "Everyone, to a great degree, is copying each other. Even very low-cost implants work fairly well. As a specialist, I do try to use brands with some longevity so that I will not be left without compatible components in the future. In addition, some companies tend to offer better prosthetic component support than others, but the variation is not huge."
Another critical decision made during the diagnostic and treatment planning phases of many cases is whether or not to opt for full-arch rehabilitation. This complex end of the implant treatment spectrum is becoming increasingly accessible to general dentists. "It seems every implant company has its own conversion method now," Birdi says. "There are so many options, so discussing them is important as more general practitioners enter this space."
The decision of whether or not to extract a patient's remaining dentition in favor of a full-arch implant-retained prosthesis is often based on the patient's comfort and preferences. "There is no universal rule for when removing teeth in favor of implant-supported restorations is the ideal solution," says Saj Jivraj, DDS, MSEd, a prosthodontist with a private practice in Oxnard, California. "Some patients with only a couple of teeth per arch can wear a removable partial denture quite successfully. Others cannot tolerate it."
When full-arch therapy is selected, Jivraj explains, everything starts with adequate diagnosis; however, surgical execution, prosthetic planning, and patient factors are important as well. "It may not be possible to immediately load everyone," he says. "We must first look at the patient's medical history. The surgeon then must evaluate the quality of the bone during surgery. There are no diagnostic tests that can be performed ahead of time that allow us to predict bone quality. If the bone is soft, the surgeon will vary the drilling protocol to ensure primary stability. I prefer a primary stability of at least 35 Ncm per implant before we immediately load. The next factor is prosthetics, which involves knowing how to fabricate the prosthesis with adequate contours, biomechanics, and occlusion. Finally, the patient must adhere to a soft diet."
Multi-unit abutments can be helpful in creating an ideal prosthesis. Jivraj notes that he placed implants for many years prior to utilizing this option. "We used to immediately load to fixture level," he says, "which essentially prevented us from being able to remove the prosthesis. Multi-unit abutments allow us to remove the prosthesis at any time because we are not impacting the implant-bone interface, and they also mitigate angulation issues, making it easier to restore patients in situations where implants have been placed in nonideal positions."
Bone reduction is commonplace for full-arch implant rehabilitations and appears to be a standard element of many systems; however, Jivraj says that performing it by default is not the way to go and that every effort must be focused on preserving bone and fabricating a prosthesis without pink. "The skill required for implant placement increases quite significantly without bone reduction, but the practitioner should always think about failure. What if significant bone reduction has been performed and the implants fail?" Jivraj says. "If patients were given the choice, would they want prosthetic gingiva or their own?"
The amount of available bone determines the ideal number of implants used in a case. Although all-on-four is a popular treatment strategy, placing more than four implants can offer important benefits if there is sufficient bone. "With more implants, we can segment the prosthesis, splitting it up into small bridges so that any complications can be more easily addressed," Jivraj says. "The all-on-four concept has a specific indication, which is when there is pneumatization of the sinuses or posterior mandibular resorption that is preventing us from placing implants
posteriorly. Oftentimes, people misinterpret the all-on-four concept as simply a more affordable but viable alternative."
Ideal restorative design is case-dependent as well. For example, Jivraj recommends 12 mm to 14 mm for screw-retained zirconia-based prostheses and a minimum of 15 mm for acrylic-titanium ones. "Keep in mind biology," he says. "The dentist should consider these factors when treatment planning and select a restoration that will require minimal bone reduction."
Upon implant placement, Jivraj prefers to keep patients in a maxillary provisional prosthesis for 4 to 6 months and a mandibular one for 3 to 5 months before fabricating the final restorations. He concedes that this is based more on anecdotal protocols and wound healing than on evidence-based science because not much exists in this area. "The numbers are based on wound healing, and I have found them to be very reasonable because we are waiting for soft-tissue stability," he says. "The last thing you want is for the gingiva to shrink and create a space underneath the prosthesis."
Complementing implant treatment strategies are the ever-evolving tools of the trade. Dentists can incorporate different elements of digital technology according to their individual preferences, but a fully digital workflow starts at the outset of a case. Digital photos, preoperative digital impressions, cone-beam computed tomography (CBCT) scans, facial scans, and even videos can all be part of the diagnostic phase. "You can digitize a patient from the start in a way that was never possible previously," Birdi says.
During the treatment planning phase, patient communication can be taken to new levels with these diagnostic tools because digital smile design allows patients to view proposed treatment options within their own faces. "That is really impactful and powerful," Birdi says. "Gaining approval before you pick up a scalpel or a bur is so important." He compares it to building a house. The patient wants to see the final result at the beginning, not just the implant foundation, and CAD/CAM software allows the dental team to execute all phases with that final result in mind. "With the restoration designed in three dimensions, we can plan implant positions, implant sizes, depth of placement, any necessary grafting, and more," he says.
The provisional restorations can be designed in advance, and eventually, integration can be checked digitally. Then the patient can be digitized again, and the data can be sent to the laboratory to fabricate the final restoration. "The power of digital dentistry, especially for implant dentistry, is in communication with the patient, communication between clinicians, and communication with the laboratory," Birdi says.
Clinicians should research products before investing in them. For example, Birdi notes that almost every intraoral scanner on the market works well for cases with one to three implants, but more complex cases, such as those involving full-arch therapy, require more accuracy. "The key is having color," he says. "Color allows your laboratory technician to really see margins and other elements much better."
How much of the digital workflow a clinician chooses to implement should depend on practice-specific factors. Another key is collaboration with the laboratory. "Coordinating your software and your scan bodies with what your laboratory uses is important to ensure a continuous workflow," Birdi says. "Laboratory support in a digital workflow is monumental. Laboratory technicians need to be involved from the very beginning of cases because they are the ones making the teeth, and the teeth are ultimately what the patients want. They also usually know a lot more about the digital workflow than many dentists do. Only providing the laboratory with an impression and asking them to finalize it is a disservice to your patient and to the profession."
Guided Surgery and Robotics
Perhaps the most advanced type of digital technology for implant dentistry is guided surgery. This technology provides a level of precision that is accurate to less than a millimeter, and that can be critical for some cases. "Guided surgery and robotics are the future," Birdi says.
Static guided surgery involves the use of physical surgical guides, which are often 3D printed, for implant placement. Alternatively, dynamic camera-based guided surgery involves the use of software that provides real-time guidance during placement. Although the former can limit versatility during surgeries, the latter lacks the assured precision associated with a physical guide. The benefits of both can be combined, however, with the use of robotics.
"The human body is not perfect, so a variety of reasons could cause you to want to change your plan interoperatively, but the limitation of dynamic camera-based guided surgery is that it is essentially freehand," says Sundeep Rawal, DMD, senior vice president of implant support for Aspen Dental. "Robotics offers the versatility and flexibility to change your plan interoperatively plus haptic guidance and the physical boundaries of the robot restraining the handpiece's movements."
According to Rawal, a conventional flapless procedure using a static surgical guide may not be best for all cases; however, some form of guided surgery should be helpful in every operating situation. He adds that the ROI, particularly for static guides, is tremendous. "It is 100% cost-effective," he says. "Systems are available for less than $10,000, and if a surgical guide saves 30 minutes of chair time, that is real money in the mouth. For some of the more advanced technologies involving camera-based navigation and robotics, you need to establish what type of surgery you are doing for the ROI to be significant. For complex full-arch cases, the time savings, predictability, and ability to provisionalize are significant. We continue to build the case for that."
Helping build that case, the applications for robotics continue to expand. "Regarding immediate extraction and placement," Rawal says, "there is a lot of variability when you take out a tooth that may make you want to change your strategy during surgery. Robotics really lends itself to that situation. Now, we are also looking at full-arch implant placement, zygomatic implant placement, new capabilities from the standpoint of bone reduction, and more."
Rawal anticipates that robotics will eventually become the standard for guided surgery. "The reality is that the ability to use automation to create precision, predictability, and repeatability in what we do is the holy grail of how technology is changing dentistry," he says. "If I have one plan and 10 different operators using dynamic camera-based navigation, I could get 10 different results even though the computer is telling them all what to do. With robotics, I could take that same plan and get the same exact result with 10 different operators because the robot controls the haptic guidance and the physical boundaries of the system."
Regardless, the role of the clinician, although perhaps changing, is unlikely to be eliminated in the foreseeable future. "We are not at a point where artificial intelligence can determine the ideal implant placement," Rawal says. "Technology is a great tool that allows us to do our jobs better, faster, and more predictably; get better outcomes for our patients; and save time and money. However, it does not replace clinical experience. The implant surgeon's role will evolve from, ‘I am a good operator' to ‘I am a good diagnostician and am experienced at managing complications.' No matter how advanced our workflows and technologies become, the reality is that the medium we are working with is the human body, and it is an imperfect medium."