Cleansability… How Did We Forget?
Alternate solutions to screw-retained implants fabricated with acrylic
By Arian Deutsch, CDT
Cleansability: Interestingly, any dictionary search or spell-check software will not recognize the term as a word. In fact, as the author wrote this article, the Pages application continued to strongly suggest that the words cleanse and ability or the single word cleansable should be used.
However, in the dental field, numerous journals utilize the term cleansability to refer to the ability to cleanse a restoration or prosthesis, specifically the patient’s ability to do so depending on their individual dexterity. A patient’s ability to maintain good hygiene regardless of the particulars of the specific restoration is important.
Particularly when it comes to implant-supported restorations, a shift has occurred in recent years to creating definitive prostheses that are screw retained — therefore not removable by the patient — and fabricated with acrylic as the chosen material.
The Perfect Storm
The 1991 Perfect Storm, also known as the The No-Name Storm, was a nor’easter that absorbed Hurricane Grace and ultimately reverted back into a small unnamed hurricane late in its life cycle.1 A wave height of 100.7 feet was recorded off the coast of Nova Scotia, the highest ever recorded in that province’s waters. In the middle of the storm, the now well known Andrea Gail sank, killing its entire crew of six and becoming the inspiration for the book, and later movie, The Perfect Storm.
Is this concept of the perfect recipe for disaster relatable to the dental field? Is dentistry starting to see the disastrous results of a unique combination of anatomy, circumstances, and treatment protocols when it comes to screw-retained acrylic hybrid prostheses? Have a big-business approach and corporate greed pulled laboratories and the dental team into the dental equivalent of the Perfect Storm? The author will ask the reader to decide.
Listen to History
Most dental professionals who have knowledge of the history of dental implants will admit that most early implant restorations were not very hygienic.2,3,4 Much of the early work pertained to solutions that were not patient removable. However, in many cases there exists a need to restore not only the dentition but also associated gingival architecture and supporting structures where osteoclastic bone resorption has left an obvious impact. Since such cases may require ridge-lapping and soft tissue replacement, are screw-retained acrylic hybrids in concert with CAD/CAM titanium milled bars the answer?
In many cases, the answer is no, in the author’s opinion. Acrylic, at its best, is still a porous material when compared to other dental materials such as porcelain, zirconia, etc., and ideally, acrylic restorations should be fabricated as patient removable if they are to be hygienic.
How Cleansability Was Forgotten
It has been said that many things old undergo a rejuvenation at some point, and this can apply to fads in the dental world. Sometimes concepts are repackaged in a very attractive way, but at their core they remain the same. One such concept is the immediate loading and screw retaining of an acrylic hybrid prosthesis that is strengthened by a CAD/CAM titanium milled bar.
This concept has been very cleverly repackaged and made attractive to surgeons, restorative dentists, and laboratories in the last 10 years, but is it really the best approach?
Additionally, is it a solution that should be marketed to the masses, or is it a smaller percentage of patients who can actually realize any benefit from this solution?
Author and filmmaker Wayne Gerard Trotman recently wrote, “Instead of loving people and using money, people often love money and use people,”5 and that seems appropriate in this situation.
Dental companies and corporations are monetarily driven entities, like most corporations. So it is appropriate to ask as an integral part of the dental team, when called on for direction, guidance, or advice on a particular implant case: Are decisions being influenced by popular solutions that seem to be very profitable, or are they influenced by experience, and what will benefit the individual patient the most?
Back to Basics
The author has observed a renewed interest in an even older, established concept: removable telescopic implant solutions, which by their very nature are extremely hygienic but also very acceptable to patients because they are highly retentive and offer the patient security and cleansability. In fact, the author has seen many clinicians, after being educated regarding this telescoping implant solution, finding patients who were previously not satisfied with screw-retained acrylic hybrid solutions, and converting these cases to implant telescopic cases.
Telescopic prostheses date back to Professor Arnold Gaerny’s early work. In the early 1970s, Gaerny published a book documenting clinical and technical work he performed in the 1950s. At that time his concept involved paralleling fixed and removable milled work to avoid open interdental spaces (Figure 1).6 Figure 2 shows a case Gaerny had parallel milled that remained obviously cleanable 13 years later.
Case in Point
A patient presented with five maxillary implants (MIS) to which custom abutments were attached, supporting a cement-retained bridge, and two recently placed posterior implants (MegaGen USA, megagen.us) that were not yet connected (Figure 3).
The prosthodontist provided a great deal of information at the first step, including casts of the implant abutments, bridge in place, implant-level verified cast, and opposing cast (Figure 4 through Figure 8).
Additionally, patient photos and expectations were provided. An initial analysis of the photos and models revealed that a great deal of planning was lacking in the initial porcelain bridge solution, and a large discrepancy existed between the tooth positions of the porcelain bridge and the proposed tooth positions according to an in-depth edentulous cast analysis (Figure 9). This was confirmed by patient photos, which presented a lack of any buccal corridor (Figure 10).
More Is Better
Regarding information, more is better. Due to the immaculate condition of the impressions that were provided, the laboratory was able to make a cast transfer accurately and quickly by mounting the existing cast of the maxillary bridge against the antagonist cast and creating a silicone putty index (Matrix Form 70, anaxdent North America, anaxdentusa.com) (Figure 11). This index was then used to cross-mount the verified implant-level maxillary cast to the antagonist cast using the hard palate as a solid reference (Figure 12).
This approach enabled the dental team to perform a bilaterally screw-retained try-in with teeth in wax at the second patient appointment, completely avoiding centric and vertical recording (Figure 13 and Figure 14).
The wax try-in clearly illustrated the contrast between the previous cement-retained ceramic bridge and the newly proposed tooth positions. With the addition of a high-quality artificial dentition, using five-layer PMMA (artegral, Merz Dental, merzdental.de), the dental team and the patient could realize a vast improvement. A natural smile was restored, and natural-looking surface texture returned to the patient’s smile (Figure 15 and Figure 16).
Telescopic Protocols
After tooth positions are approved and a centric and vertical record were confirmed, a phonetics and function test was performed, and a double scan was carried out to enable design of the primary telescopic abutments within the volume of the approved tooth positions (Figure 17). Scan, design, and primary milling were performed by Dental Creations Laboratory Inc. in Tucson, Arizona.
The abutments were milled in zirconia, sintered, and hand-milled with a high-speed water turbine and a series of five progressive diamond milling burs down to 4 microns so that no microfracturing took place (Figure 18 and Figure 19). The abutments were then hand polished on the hand mill with a series of three dry diamond impregnated polishers, which were consistently dressed at either 0° or 2°, depending on the specific case, thus ensuring a perfectly polished surface, with walls remaining intact at the desired 0° or 2°.
Galvano Process
One of the most important aspects of a telescopic prosthesis is the fit tolerance from secondary to primary component. No technology that is currently employed is quite as accurate as the Galvano method, or electroforming of a high-purity gold (99.9%) to the primary telescopic abutment surface. This method achieves a 4- to 5-micron fit consistently.
This process can be carried out in both a direct and indirect method, either directly to the abutment surface or to a duplicate die using duplicating silicone and Fujirock® IMP (GC America Inc., gcamerica.com). Once the Galvano process for this case was completed, the electroformed abutments or dies were removed from the Galvano unit (Gammat® free, Gramm Technik, gramm-technik.de) and separated (Figure 20). The remaining silver lacquer residue was then removed with 40% nitric acid solution under ultrasonic waves (Figure 21). The secondary Galvano telescopes were refined and fit to the primary zirconia telescopic abutments (Figure 22).
Tertiary Structure
A tertiary structure served to cement the gold copings, and as a substantial reinforcement lending a great deal of strength to the prosthesis. It was digitally designed within the volume of the approved prosthesis volume, which was checked in wax (Figure 23). The tertiary structure design, which was scanned and designed by Alexander Wünsche, CDT, of Zahntechnique in Miami, Florida, was then transmitted to an SLM production facility (Bego USA, begousa.com) and the selective laser melting process was completed, providing a very accurate tertiary structure with a perfect cement gap (Figure 24).
The tertiary structure can be cemented on the verified cast or intraorally to the gold secondary copings (Figure 25 and Figure 26). Once this was completed, a processing duplicate was made using duplicating silicone (GC America Inc.), and a processing duplicate was vacuum mixed and poured in a type IV resin reinforced gypsum (Fujirock IMP, GC America Inc.).
Final Processing
Another critical aspect of restoring a patient’s dentition is creating lifelike, natural-looking tissues. Many materials are on the market, and newer materials are becoming available all the time. In the author’s experience, utilizing a variety of colorized heat-cured acrylics provides a very natural appearance and is durable and color stable long term. It is important to select an acrylic that has a high impact resistance. Nature-Cryl® Super Hi Impact acrylics (GC America Inc.) can be traditionally press packed or injected and demonstrate such properties. The acrylic tissue can also be modified by removing the artificial veins, and placed and blended strategically to mimic gingival tissues very closely.
One technique that has been very successful utilizes disposable syringes in order to place the differing colors of acrylic exactly where desired (Figure 27), and then to manipulate with a Kolinsky brush to blend the colors. This technique prevents transition lines that may look artificial.
Conclusion
The patient in this case experienced a vast improvement in esthetics, comfort, and cleansability (Figure 28), with a very minimal volume of acrylic, which only replaced the dentition and structures that were lost (Figure 29).
Telescopic implant prosthetics have a long, rich, well-proven tradition in Europe.6 Compared to the current screw-retained acrylic hybrid solutions available, the implants offer a compelling alternative to such solutions and warrant further examination for use in the implant market. For the purposes of this article, special focus was placed on the cleansability aspect of telescopic implant prostheses.
However, many additional benefits to this solution exist, such as less restorative space requirements, implant angulation corrections without need of an angled multi-unit abutment, and easy and economic repairability. The author plans to cover these and other benefits in depth in future articles and hands-on courses.
Disclosure
The authors had no disclosures to report.
References
1. Schnitman PA; Wöhrle PS; Rubenstein JE. Immediate fIxed interim prostheses supported by 2-stage threaded implants: Methodology and results. 1990 J Oral Implanto|(16; 2,; 96-105) Brånemark P-I, Svensson B, van Steenberghe D. Ten-year survival rates of fixed prostheses on four or six implants ad modum Brånemark in full edentulism. Clin Oral Impl Res 1995; 6:227-231. Schnitman PA; Wöhrle PS; Rubenstein JE; DaSilva JD; Want NH. Ten-year results for Brånemark implants immediately loaded with fixed prostheses at implant placement. Int J Oral Maxillofac Implants. 1997|(12; 4; 495-503)
2. Gaerny, Arnold. Removable Closure of the Interdental Space (CIS). Quintessenz, 1972.
