Statistics indicate that the average dental office in the United States performs thirty crown preparations per month. Considering that most offices operate on a schedule of four patient contact days per week, the average office is performing roughly thirty crowns per month on a sixteen day per month work schedule. This translates to approximately two crown preparations per day in the average office. Of course, that also translates to the need for offices to also cement approximately 2 crowns per day as well. With that statistic in mind, it is easy to see that proper and efficient cementation of fixed prosthetics is a tremendously important part of a general dental practice.
Fixed prosthetics is a large part of any dental practice and it is one that is intrinsically dependent on chemistry provided by a third party to ensure clinical success. There are many steps that must be performed adequately for a crown to experience long term success. The walls must be tapered, but over tapering provides lack of retention. The walls need to exhibit parallelism, but cannot have undercuts or be too parallel. The occlusal reduction must be adequately reduced to allow for proper thickness of the prosthetic material, but over-reduction can reduce wall length, which in turn reduces retention. The margin needs to be clear, concise, and easily identified by a software or laboratory technician. In short, an operator can perform a textbook preparation, but the long-term clinical success of the crown depends greatly on the ability of the cement to keep the prosthesis sealed and held securely in place.
The problem of past cementation systems
In the past, cements were soluble in oral fluids and over time these materials could “wash out” as they absorbed fluids, softened, and crumbled away. This could result in margins that were, despite the best efforts of the operator, microscopically open. This created areas where plaque and its resultant bacterial inhabitants could accumulate. This accumulation of bacteria and the acids they produced often resulted in marginal breakdown, recurrent decay, and necessitated replacement of the restoration.
These cements were not incredibly retentive on their own. Because of this, many of the principles of crown preparation were designed to aid in the physical retention of the prosthesis. The principles of 5° wall taper, parallelism, and gingival bevels were created and then taught to aid in and increase mechanical retention. While parallelism and 5° taper are still excellent concepts and should, whenever possible, be applied today, the practice of gingival bevels is contraindicated in many of today's aesthetic materials. Gold and porcelain fused to metal restorations benefit from bevels due to the fact that the metals retain strength even when they are thin. However, aesthetic materials such as lithium disilicate and zirconia will fracture along the marginal interface if used for preparations with a gingival bevel. Those types of materials require a certain amount of bulk to resist fracture. This is why adequate tooth reduction is so critically important with certain materials.
Modern cementation solutions
The amazing success rate that accompanies today’s fixed prosthetics is in no small way related to the incredible progress that has been made by the chemists who create today’s bondable dental cements. Materials such as VOCO’s Bifix QM have contributed to a new generation of materials that provide superior clinical results and give the dentist peace of mind that they have provided a material that will predictably remain in place.
The principle of a beveled margin was two-fold. The first was to increase retention, while the second was to create as small a gap as possible at the tooth-restoration interface. Due to the solubility of early cements, this was a needed part of the procedure. A shoulder or heavy chamfer margin could lead to more rapid breakdown when the cement washed out.
Bifix QM is a resin cement. That means it is in the same family of materials as composite. Because of this, Bifix QM has similar physical properties as materials that are used for direct restorative procedures. One of the principal benefits of bondable resin cements is that they are not easily soluble in oral fluids and because of that, they do not wash out. Instead they stay in place and seal the marginal interface, keeping bacteria out and helping to prevent recurrent caries from developing at the tooth-restoration interface.
Another benefit of using Bifix QM is its dual cure component of the material. While it is an outstanding material for permanent luting of dental prosthetics, it shines in other applications as well. It is not uncommon for the practitioner to be faced with situations where endodontic therapy followed by a prefabricated post and bonded core build-up are needed.
These clinical situations present challenges for the doctor who is dealing with multiple aspects of material applications. One of the biggest challenges in adhesive dentistry is control of the operative field. Blood, saliva, and crevicular fluid are all potential contaminants whose effect can contribute to compromising a procedure, or even clinical failure. In these situations, efficiency becomes intrinsic to success. Materials that require multiple steps or extended working times increase the likelihood of contamination.
Bifix QM provides ideal characteristics for these challenging clinical situations. The material is dual cure which allows the polymerization of the material to be initiated by the curing light. This allows immediate sealing of any margins or circumferentially around a bonded post. With the outermost layer polymerized and sealed, contamination of the bond of the post becomes a non-issue. The practitioner can also be assured that the self-cure aspect of the material ensures that even deep within the prepared post space where light cannot penetrate, full polymerization occurs.
Bifix QM is also packaged with VOCO’s Futurabond DC. This product is a one-step dual cure self-etching adhesive. Since it is a self-etch product, it provides for an efficient and reliable method of etching and bonding tooth structure prior to the placement of Bifix QM. A total etch approach would take more time, thereby increasing the odds of contamination. Also, both products have high bond strengths, high flexural strengths, and work well together, which ensures the long term longevity and stability of the restoration. Flexural strength is significantly important as a “brittle” cement will begin to degrade when forces are applied. The oral cavity is a complicated environment and powerful forces can be applied from many directions. A high flexural modulus means that when these forces are applied, Bifix QM flexes like natural tooth structure, which works to provide long term stabilization of the restoration.
Cleanup is easily accomplished since the material has a long elastic gel setting phase. This allows for easy removal of excess material with an explorer or scaler. This longer gel phase allows the operator to consistently clean all accessible margins as well as flossing interproximal contact areas without the concern of the material setting before cleanup can be completed. The gel phase means the practitioner can work without the stress of the excess material needing to be removed with ultrasonics, which can be a concern with materials that exhibit a shorter gel phase than Bifix QM.
Once the margin is cleaned, the curing light is used to photopolymerize the material at the margins, which seals it from the oral environment.
Conclusion
Bifix QM is material agnostic, meaning it can be used to permanently cement any indirect restorative material. Whether the practitioner chooses ceramic, zirconia, lithium disilicate, PFM, metal or composite, they have the comfort of knowing Bifix QM can handle them all with ease. There are many material choices available to today’s doctor. Knowing which material to use in each unique case can be 
challenging. Those choices become even more daunting when the doctor then needs to inventory and properly use multiple permanent luting solutions as well.
In the busy environment of today’s dental office, there is no need to learn to master multiple materials and multiple luting solutions. The doctor can reach for one product, Bifix QM, and be assured of material compatibility, ease of use, easy clean up, and long term clinical success.
Doctor Flucke was born and raised in Kansas City. He received his Doctor of Dental Surgery degree from the University of Missouri - Kansas City in 1987. He has practiced in Lee's Summit since 1989 and was pleased to open his new state of the art facility in 2007.
