The Time for Short Is Now: Today’s Short Implants and Why You Should Give Them a Chance

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Short implants are currently experiencing a huge wave of commercial and clinical interest, with large implant companies like Nobel Biocare, Straumann, Dentsply Sirona, Biohorizon, and Zimmer Biomet all introducing their own offerings in recent years. Defined as implants with a designed intrabony length (DIL) equal to or less than 8 mm, short implants once occupied the far fringe of the implant market. Their recent rise to the mainstream may give some clinicians the false impression that these lengths of implants are new and relatively untested, but in reality, science established the value of short implants much earlier than the market did. Dr Douglas Deporter, a clinician and researcher who has devoted more than 30 years to the clinical study of short and ultra-short implants and who is the editor of a book on the topic, reflects on why he has dedicated his career to short implants. He also explains why their surge in clinical prominence today is wholly deserved.

A Periodontist’s Path to Implant Dentistry

“My interest in dental implants started almost 40 years ago,” explains Douglas Deporter, DDS, Dip Perio, PhD. “In 1979, I was a newly appointed assistant professor at the University of Toronto (U of T). The head of prosthodontics at my faculty, Prof George A. Zarb, proposed a site visit to investigate firsthand the rumors that an orthopedic surgeon by the name of Per-Ingvar Brånemark and his colleagues in Göteborg, Sweden, had developed and were testing a pure titanium threaded dental implant for tooth replacement. I was asked to be a member of the site visit team, and hence began my involvement in the implant field. Prof Zarb later organized a replication trial of Brånemark implants at U of T called ‘The Toronto Study.’ The early findings from The Toronto Study were supportive enough by 1982 that Prof Zarb and the Brånemark camp organized the first meeting in North America dedicated to the Brånemark implant concept, called the Toronto Conference on Osseointegration in Clinical Dentistry.”

The Toronto meeting was significant in that it turned the tide on the scientific community’s opinion toward dental implants. Just 4 years prior in 1978, the US National Institutes of Health (NIH) and the Harvard University School of Dental Medicine had cohosted a conference with the intent of forming a consensus on dental implants. “The 1978 conference all but shut down interest in dental implants, which were seen by those involved as ‘snake oil treatments,'” Dr Deporter explains. “At the time, none of the participants were aware of Prof Brånemark’s work. But the impact of the 1978 conference was completely overruled by the findings presented at the Toronto meeting and the enthusiasm they generated.”

The invitation-only Toronto meeting primarily included prosthodontists and oral surgeons. Interestingly enough, periodontists were originally excluded from implant research and treatment due to the early opinion that the quality and quantity of soft tissue around implants was irrelevant. However, Dr Deporter managed to attend the Toronto meeting, and the experience changed his career path as a periodontist.

“I attended the Toronto conference with several members of our faculty,” Dr Deporter recalls, “including Prof Robert M. Pilliar, a biomaterials scientist responsible for the development of a highly successful cementless hip implant prosthetic device. Bob was intrigued by the idea of titanium dental implants, but not those like the Brånemark implant, which was a smooth machine-surfaced threaded device. Instead, he suggested to us that the same surface technology from his hip implant, which had a sintered porous surface (SPS) topography, could be applicable to dental implants and may offer some unique advantages over the threaded screw concept.”

The SPS implant that Dr Deporter and his colleagues designed and tested was fabricated from titanium alloy and had a 5-degree taper to make it similar in shape to natural tooth roots. Early animal experiments indicated that the team was on the right track: They found that the sintered surface provided a much stronger bone-to-implant interface than a threaded implant with a machine-turned surface. The University of Toronto obtained a patent for the implant and awarded a license to Innova LifeSciences to produce it. Innova subsequently applied for approval from the US Food and Drug Administration (FDA).

“As expected, the FDA expressed doubt about the short implant lengths being used,” Dr Deporter recalls. “They insisted that our clinical work be duplicated by a small group of American dentists on American patients. The American clinicians, however, wanted longer implant lengths available to use when bone height allowed them to be used. Frankly, they did not believe that our short implant could work. In order to fulfill their request, Innova produced a 12-mm-long version, 12 mm being the maximum length possible with the implant’s designed 5-degree taper angle. We tried out some of these longer ones at U of T as well and, along with the US investigators, concluded that the longer length was of no advantage and may even underperform compared with our standard shorter length.”

Early Resistance

While the Toronto meeting galvanized interest in dental implants, it did so only for one type of dental implant—the Brånemark threaded implant—and only at lengths between 10 and 20 mm. Few in the dental community were as adventurous and willing to stray from the Brånemark path as Dr Deporter and his colleagues were. Further obstructing the acceptance of short implants were problems arising from early study designs and the way their results were presented, which unfortunately became the foundation of opinion for most clinicians and researchers.

“My colleagues and I were thought from the outset to be way off base in thinking that implants could be much shorter in length than were then seen to be safe and predictable,” Dr Deporter explains. “General opinion at the time was that if Brånemark implants were available in lengths ≥ 20 mm, how could an SPS implant with a DIL of just 5 mm work equally well? The conclusion was introduced that short lengths were inappropriate for Brånemark-type implants following early applications by less experienced clinicians such as those participating in The Toronto Study. However, later research verified that short Brånemark-type implants could have high survival rates even in the posterior maxilla as long as appropriate surgical modifications were made to the placement techniques.”

“The poor reputation of short implants is—for the most part—based on early implant literature using the original Brånemark implant: A commercially pure titanium threaded screw with a machine-turned (ie, minimally rough) surface finish [References: 1, 2, 3, and 4],” says Past President of the European Association of Osseointegration and short implant advocate Dr Franck Renouard. “In each of these reports, the authors stated in their abstracts and/or conclusions that failure of short (ie, ≤ 10 mm) implants was higher than that of longer ones. This was enough to establish a dogma that was not easily challenged. However, a closer reading of these articles reveals that although the failure rates with short implants were higher, the difference compared with longer implants was less significant than the authors implied. For example, in the report by Friberg et al examining 4,641 implants, the failure rate of short maxillary implants covering everything from single crowns to full-arch reconstructions in fully edentulous patients was only 7%. Looking only at the results for partially edentulous patients in this study, the failure rate of short implants plummeted to 1.3%. Moreover, the authors stated that most of the failures were early—once short implants had been fully integrated in bone, they behaved just like longer implants. In 1991, these clinicians were not only using cylindric, machined-surface implants; they were also following a standard and identical drilling protocol for both short and standard-length implants and regardless of the bone density encountered.

“The reluctance of clinicians to use short implants persists today,” Dr Renouard continues, “and derives largely from their reading of statistical assessments of implant failure while neglecting other considerations like the patient’s sex, the size of the patient’s mouth, the risk of complications with more complex procedures, and the feasibility of such procedures being undertaken by non-specialists in a private practice setting. A quick search on PubMed in December 2016 identified 5,400 articles mentioning short implants, but the majority of articles focused on more complex solutions, relegating short implants to the rank of emergency fallback solutions only. Consequently, the mindset persists that the longer the implant, the more successful it will be both in the short and long term. Advanced, costly, and technique-sensitive collateral procedures often need to be performed to be able to use standard-length implants, such as autogenous (and other) bone block grafting, vertical alveolar ridge augmentation, mandibular nerve repositioning, and open sinus grafting. Interestingly, however, the first implants developed and tested successfully by Brånemark in the 1960s were all under 8 mm in length, and some were even shorter than 5 mm.”

One of the most important tenets of scientific research is to compare ‘apples to apples’ when comparing two things. It’s why controls are an important part of study design. Clinicians in these early studies were applying short implants in less favorable conditions than standard-length implants, but they weren’t controlling the reported data to accommodate those differences. This resulted in misleading comparisons between the efficacy of short versus standard-length implants. Hindsight and modern research also allow for the observation that the less-than-ideal machine-turned surface of early implant designs could have had a far more negative impact on outcomes than implant length.

“In 2005,” Dr Renouard states, “Hermann et al analyzed a large number of failed implant procedures and reported that short implants had usually been used in sites with low bone volume and density, whereas longer implants were nearly always placed in denser bone. This observation challenges implant length as the cause of failure. For example, did an implant in the posterior maxilla fail because of its length, or was the result caused by low bone density and the clinician’s failure to appropriately modify osteotomy preparation?”

The misleading presentation of success rates with short implants can be partially excused by simply not knowing then what we know now about important factors of success for endosseous implants. It can also be attributed in part to a phenomenon affecting all areas of research.

“The adaptation of these findings to comply with the general consensus at the time (ie, that implants shorter than 10 mm fail more often despite contrary objective data) is termed confirmation bias,” Dr Renouard explains. “This type of bias is a very common cognitive behavior: Once a decision has been made or a ‘fact’ learned, the human brain will always look for data that corroborate the preconceived notion in question and dismiss data challenging these notions. It is an unfortunate but frequent occurrence in many scientific fields.”

Current Knowledge

With the problems present in early research on short implants, where does the current literature stand? Dr Deporter’s book Short and Ultra-Short Implants provides a valuable update.

“The most common location for short implant use is currently the resorbed posterior mandible,” Dr Deporter says, “but they can also be appropriate in the resorbed anterior mandible. In a posterior maxilla with resorption or a pneumatized sinus, some short implant designs have proven to be a legitimate substitute for longer implants used in conjunction with a dedicated open sinus floor elevation and grafting procedure. Using short or ultra-short implants in this last situation greatly reduces the associated risks, patient morbidity and anxiety, and cost. One recent investigator actually concluded that there is little justification for open lateral window sinus grafting where 5 mm of subantral bone remains preoperatively because a short implant with or without minimal indirect sinus floor elevation (eg, using hand osteotomes) will often work equally well. Using short or ultra-short implants can also simplify treatment in sites with alveolar ridge undercuts that would otherwise lead to apical bone fenestrations with longer implants.”

While these may seem like specific indications, experienced clinicians will recognize that no implant size or length can feasibly be used as a one-size-fits-all solution. Short and ultra-short implants therefore represent a valuable treatment option for situations that would generally require invasive augmentative procedures in order to place standard-length implants. Short implants also present several advantages, including lower risk of neurovascular damage in the posterior mandible, lower risk of sinus damage or infection in the posterior maxilla, simpler and less invasive surgical procedures, shorter treatment times, higher patient acceptance, and lower treatment costs for the patient. Even so, many clinicians may still feel more comfortable placing standard-length implants in conjunction with adjunctive surgical procedures, even in situations where short implants have proven successful. In the book, Dr Deporter and his colleagues address some of the common concerns that prevent clinicians from using short implants.

“Until fairly recently,” Dr Deporter explains, “crown-to-implant (C/I) ratio was a major concern with short implants. From the outset of contemporary implant dentistry, it was theoretically and empirically decided that the C/I ratio should not exceed 1:1. This ratio was based on the established minimum crown/root ratio for healthy natural teeth; however, evidence has shown that due to the difference in nature between natural teeth retention and osseointegrated implants, this rule need not be applied. The perceived danger was a high levering effect at the bone crest that may result in bone microfractures and resorption. Recent research, however, has found that increasing the C/I ratio does not correlate positively with crestal bone loss, though evidence does point to there being critical upper limits for the C/I ratio that differ with different implant designs.”

Another concern is the fact that short implants cannot be treated the same as standard-length implants. Rather, a successful outcome largely depends on the clinician’s ability to correctly modify surgical protocols when placing short implants.

“Clinical data has shown that outcomes could be significantly improved by modifying standard threaded implant osteotomy preparation techniques,” Dr Deporter explains. “Preoperative evaluation of bone quality and density using CBCT can help the surgeon determine which modifications to make, which may include modified approaches such as an undersized osteotomy or a stepped osteotomy.”

Changing Perspectives

For the periodontist who has dedicated his career to the research and development of short implants, the changes occurring today are better late than never.

“Progress in dentistry is generally slow when it comes to applying research data to routine clinical practice,” Dr Deporter explains, “but it feels good to see change happening even if it has been at a snail’s pace. I have always felt that short would triumph in the long term, particularly when colleagues in countries other than the US started replicating and expanding upon our findings with SPS implants. Unfortunately, however, many dental practitioners—particularly in North America—still look to industry for answers rather than seeking out published independent research data. Luckily, most implant manufacturers have now seen the light and begun to produce short implant models, some as short as 4 mm. The fact that so many companies now produce short implants is a clear indication that there is a perceived high demand for them.”

However, there is also the potential to move backward and lose the ground so painstakingly gained. “I can only hope,” Dr Deporter says, “that any manufacturer that provides short implant options will have sufficient clinical trial data beforehand to provide defined proper protocols and limitations specific to their offerings. Short implants can be successful, but only if protocols are strictly followed and if clinicians pursue adequate information before using them. My fear is that the progress made to date may be undermined by high failure rates from clinicians who fail to understand that shorter does not necessarily mean simpler.

“Did I ever waver in my belief that short was good?” he continues. “That’s easy to answer: No. As they say, the proof is in the pudding.”

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Douglas Deporter, DDS, Dip Perio, PhD, has been a full-time member of the Faculty of Dentistry at the University of Toronto since 1976. He has been involved in clinical research in implant dentistry for over 30 years and has published extensively on short and ultra-short implants, particularly those with sintered porous-surfaced (SPS) topography. He was coinventor of the original SPS implant (Endopore), the patent for which was assigned to the University of Toronto. Dr Deporter has given more than 140 invited international presentations. He also maintains a part-time private practice limited to periodontics and implant dentistry in Toronto, Ontario.

 

Short and Ultra-Short Implants

Edited by Douglas Deporter

Research has shown that short implants are not only a viable option but oftentimes a superior one that carries fewer risks for the patient and dentist, especially in resorbed jaw sites. As clinical trials continue to underscore the safety and efficacy of short implants, more dentists are considering their use with real interest, and this book provides the information clinicians need to incorporate short implants into their own practice. The book reviews the clinical effectiveness of short implants and then describes treatment protocols for the various types of short implants and their placement in different areas of the mouth. Case presentations demonstrate the recommended techniques and showcase the results.

168 pp (softcover); 334 illus; ©2018; ISBN 978-0-86715-785-7 (B7857); US $85