What Dogmas in Implant Therapy Do You Struggle With, Either Surgically or Restoratively?
Jeanne M. Salcetti, DDS, MS; Dean E. Kois, DMD, MSD; David French, DDS
Single-Tooth Dental Implant Therapy
One of the many dogmas in implant dentistry is that single-tooth dental implant therapy is an easy "no-brainer." However, the implant literature is fraught with cases that show unfavorable results. Often times, before doing implant surgery dentists could put themselves in better position to achieve optimal outcomes if they collaborated and communicated more effectively with their surgical specialists. Communication is fundamental in working with both patients and fellow colleagues.
As a periodontist in private practice for 24 years, one of the greatest challenges in implant dentistry that I experience, as do my surgical and restorative colleagues, is communication-or more specifically, inadequate communication and its subsequent consequences.
The case presented (Figure 1 through Figure 3) highlights the impact of poor communication by the restorative dentist to the patient. The patient was referred to the practice for tissue grafting due to poor esthetics. Bone and soft-tissue recession were present around a lateral incisor adjacent to an anterior implant. Also, dark tissues presented on the facial aspect of the implant crown. The referring restorative dentist (who placed the anterior implant and crown) had not told the patient of any concerns with the health of the implant or the supporting hard and soft tissues around it.
After completing an evaluation both clinically and radiographically and identifying the retreatment challenges, I proceeded to have the dreaded conversation with the patient. Unfortunately, she was under the assumption based on her communication with the referring dentist that her esthetic issues could be resolved with a tissue graft. This, however, was not going to correct the problem. While certainly appreciative of the referral and the "team" approach to care, I had to demonstrate to the patient the challenges and limitations involved and provide what I deemed the best treatment options available in order to achieve as close to an ideal smile as possible. These findings and discussions with the patient were then shared with the referring dentist.
Whether treating simple or difficult cases, a communication strategy that can be a blueprint for success is to provide the "buyer's journey" concept. It has three stages that are equally important in discussion:
Awareness stage: The patient develops an interest or concern and, thus, becomes aware of his or her condition, problem, or desire.
Consideration stage: After the dentist has thoroughly diagnosed and planned the necessary care, the patient now has all of the pertinent information and a clear definition of the problem. All options for correction have been explored, which might include further consultation with referred specialists.
Decision stage: The patient now chooses the strategic solution and is prepared to make a purchase decision.
This approach allows patients to fully participate in all discussions with the dentist and specialists and have clear expectations for their treatment outcomes. As clinicians, our communication must be easy to follow and understand. Poor communication that can prompt a myriad of negative emotions from patients must be eliminated. It is incumbent on restorative dentists to properly diagnose a patient's problems and communicate them so that the patient understands the magnitude of the situation. Patients should never be "blindsided" by discussions with specialists.
Never assume that a single-tooth dental implant is a "no-brainer." Remember, collaboration plus communication equals success.
The decision to splint implants together, in my view, should have more to do with mitigating mechanical disadvantages for the restoration and less to do with creating a biologic advantage for the implants themselves. Traditionally, splinting has been utilized to control load. A more detailed look shows there are numerous long-term studies that assess the success and survival probabilities of dental implants. The literature is rather clear that mechanical sequelae are three to four times more likely to occur than biologic sequelae.1In short, some component will usually break or come loose far more often than the implant will fail-whether splinted or nonsplinted.
In fact, very little quality science exists that supports implant failure due to occlusal overload or excessive crown-to-implant ratios. Historically, when turned implants were being used without newer nano surface coatings and more aggressive thread patterns it was easier to ascertain whether an implant was well integrated or not. The traditional osseointegration curve from Raghavendra et al showing primary to secondary stability2 does not apply in the same manner today. Newer implants do not experience the dip in primary stability at about 3 weeks; rather, they stay at high stability and secondary stability (osteointegration) catches up. I believe many of the implants that clinicians think fail today because of occlusal overload were actually never well integrated from the outset. Moreover, all load-related implant studies that have demonstrated implant failure associated with occlusal overload are non-human studies. If occlusal overload was a primary source of implant failure, then chipped porcelain, loose screws, implant fractures, and implant failures not always being the most distal implant where load is the highest would all be rare occurrences. This is clearly not what is typically seen in clinical practice.
Mechanical failures happen more frequently than biologic ones. There are several indications for splinting implants in my practice. First, path of insertion/implant positioning concerns may dictate whether or not to splint. Many times cervical embrasures, contacts, and ideal anatomy can be achieved more predictably with splinted units. Another indication for splinting is narrow-diameter implants in the posterior. For molars, when these implants are used, larger cantilever force vectors off of the long axis of the implant may result. This will stress the screw-joint geometry (micromovement) and can lead to screw-loosening events or potential implant fracture. This can be overcome by splinting to reduce micromovement. This enhances the anti-rotation features in the restoration. One reason to use narrow implants in the posterior is to minimize the need for grafting protocols in some clinical situations. By using 4-mm implants to replace two molars, splinting them together allows clinicians to mitigate micromovement from the cantilevers off of the implant, enabling more normal tooth proportions to be designed.
While I do not splint natural teeth to implants in my practice, it certainly is a possibility. A critical appraisal of the situation and an understanding of the science are essential. This approach can work with careful case selection, specific laboratory parameters, and a willingness to accept some sequelae like intrusion and mobility of the natural teeth. Survival probabilities of splinting natural teeth/implants are similar to implant/implant splinting when conditions in the mouth are close to optimal.3If there are too many parameters that can impact an outcome that the clinician cannot control, or if risk cannot be minimized, this option shouldn't be used.
Splinting Implants; High Insertion Torque
Two issues stand out to me regarding implant therapy philosophies. The first is whether or not to splint posterior dental implants. External hex machined-surface implants had limited bone contact and weak screw-joint stability, so splinting was considered customary to prevent implant loss and screw loosening. Modern micro-rough implants have improved osseointegration and stable internal connections, and, therefore, many opinion leaders suggest splinting is no longer required. Although at least one study suggests equivalency,4 my opinion is that posterior implants should always be splinted together. Overloaded implants risk rapid bone conversion to connective tissue,5,6 and this loading is magnified at crestal bone; however, finite element method studies have shown this effect is reduced when implants are splinted.7-9
In a study that is currently in progress, the author's internal analysis of 10,387 implants followed for 1 to 15 years revealed 20/41 post-prosthetic failures occurred as "sudden implant loss due to overload," and 19/20 of these were unsplinted posterior implants in otherwise healthy function >5 years suggesting long-term data is needed. Mendonça's long-term study intimates single implants in the posterior region are susceptible to high force and micromotion more so than physiologic limits.10 Moreover, splinting is now clearly supported by a recent meta-analysis of 4,219 implants followed on average over 7 years that reveals a threefold failure rate for unsplinted posterior implants.11
Another debatable issue is high insertion torque (HIT). Traditionally, torque on insertion as an indirect measure of primary implant stability typically did not exceed 45 Ncm, because orthopedic literature and dental histology warned that excess compression risked osseointegration.12,13 Torque on insertion provides primary stability through mechanical fixation, then after 2 weeks a "stability dip" occurs until secondary stability develops via osseointegration. The dip represents a zone of necrosis that develops after surgical and compression trauma, and HIT has been shown to double the zone of necrosis and impair secondary stability.14,15Further histology support has shown osteotomy under-preparation (no tapping) compromised osseointegration of tapered implants with significantly lower bone-to-implant contact and more crestal resorption in the HIT group.16Insertion torque of 30 Ncm to 50 Ncm is proven and accepted for immediate loading, while <25 Ncm may risk mobility-related failure in single-unit cases.17,18
HIT is achieved by under-preparation and use of tapered implants and, more recently, aggressive thread designs. Market demand for immediate loading has pushed the "limit" to ≥70 Ncm. HIT up to 70.8 Ncm to 176 Ncm has been reported to show "no difference" compared to controls of 30 Ncm to 50 Ncm.19 However, limitations in this 1-year nonrandomized, non-blinded, clinical (non-histologic) study were that it did not report implant locations, the control sample was small (nine control versus 42 HIT implants), and the standard deviation was large; thus, the fact that there was "no difference" between groups is not surprising. There was only average bone data with no outlier reporting, yet the only two implants with complications were both in the >70 Ncm group. The results also showed that from 3-months to 1-year follow-up HIT implants had nine times more bone loss (<50 Ncm = 0.06 mm versus >70 Ncm = 0.52 mm). More study, including histology, is needed to accept the HIT concept.
HIT may add risk, with one study reporting lower implant survival for HIT (83%) versus controls (96%).20 HIT may not even add benefit, because implant stability quotient values and torque only correlate well up to 50 Ncm, but at >50 Ncm the increased torque does not increase stability.21 Considering that insertion torque >50 Ncm is supported by only a few clinical reports and lacks histologic validation, and there is clinical and histologic evidence that 35 Ncm to 50 Ncm is suitable for immediate loading, >50 Ncm may represent added risk with no reward.
Jeanne M. Salcetti, DDS, MS
Former 3-Year Chair, American Academy of Periodontology Oversight Committee in Continuing Education; Private Practice, Colorado Springs, Colorado
Dean E. Kois, DMD, MSD
Instructor, Kois Center, Seattle, Washington; Private Practice, Seattle, Washington
David French, DD
Private Practice specializing in Periodontics, Calgary, Alberta, Canada
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2. Frost HM. Wolff's Law and bone's structural adaptations to mechanical usage: an overview for clinicians. Angle Orthod. 1994;64(3):175-188.
3. Nagasawa M, Takano R, Maeda T, Uoshima K. Observation of the bone surrounding an overloaded implant in a novel rat model. Int J Oral Maxillofac Implants. 2013;28(1):109-116.
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6 HL Huang, JS Huang, CC Ko, JT Hsu . Effects of splinted prosthesis supported a wide implant or two implants: a three-dimensional finite element analysis. Clin Oral Implants Res. 2005;16(4):466-472.
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18. Baldi D, Lombardi T, Colombo J, et al. Correlation between insertion torque and implant stability quotient in tapered implants with knife-edge thread design. Biomed Res Int. 2018; doi: 10.1155/2018/7201093.