CAD/CAM’s Influence on Indirect Restorations: The “Tipping Point” Has Been Reached

Chairside CAD/CAM: The Material Revolution

Not long ago porcelain-fused-to metal (PFM) was the primary means for achieving an acceptable cosmetic result for posterior teeth. CEREC^® (Dentsply Sirona, dentsplysirona.com) became the"disruptor" in 1985. Radical for its time, it used a digital imaging device (intraoral camera with a sensor), computer-aided design, and connected milling unit for same-appointment delivery of an intracoronal restoration milled from a silica-based ceramic block that needed adhesive luting to reinforce the material. Using the acronym "Chairside Economical Restoration of Esthetic Ceramics," this "disruptive" business model challenged traditional materials and fabrication methods. Despite the profession's wariness of the ceramic materials, the relative infancy of dental computerization, and uncertainty over costs, it eventually became a staple for dental care. Over the past 34 years, CAD/CAM technology has been continuously validated accompanied by documented long-term outcomes.^1-4

Today there are numerous platforms/systems available for chairside CAD/CAM, with estimates approaching 20% saturation in the United States, the largest world market.⁵ Available materials include polymethyl methacrylate (PMMA) acrylics, composites, glass-ceramics, hybrid ceramics (polymer based), and polycrystalline ceramic (zirconia). Significantly, these wide-ranging choices offer unique opportunities for dentists to select materials specific to the needs of the patient rather than adapting the patient to the gold and PFM restorations of the past. Zirconia, whose very existence is owed to CAD/CAM technology, is now one of the most widely prescribed materials.⁶ By using computer design and subtractive process manufacturing (milling), any dentist prescribing zirconia can be considered a "digital" or "CAD/CAM" dentist.

Dental Laboratories: The Business Transformation

"Business is business" and dental laboratories have taken the lead in terms of CAD/CAM manufacture. During any "disruptive" period, businesses must confront change and be willing to adapt to survive. In the transition to digital CAD/CAM dentistry, competition from offshore labs, dentists' downward pressure on laboratory fees due to declining reimbursements, increasing costs of operation, upward pressure on laboratory labor costs, and a shrinking skilled labor pool were serious challenges to the profit structure for laboratories.To maintain and even increase profitability, lab businesses had to be "better at a lower cost" while simultaneously maintaining or even increasing value for their services.Consider Walmart and its disruptive effect on retailers, or Amazon on brick-and-mortar stores. The adaptation andincorporation of digital CAD/CAM technologies challenged old laboratory business models common tomany small labs much like small stores, with the result being significant consolidation.While nearly 35%of labs have beeneliminated, productive capacity paradoxicallyhas increased.⁷ Higher-quality production is now coupled with lower product costs (lab fees) inflation adjusted from 10 years ago, and has reestablished the "value proposition" by way of digitalization and CAD/CAM.⁸ To address market forces undermining their profitability and very existence, laboratories were forced to invest in digital technologies.⁹

Modern dental labs are unrecognizable from the past. Digital design and manufacture have replaced many of the tasks requiring human labor, which is expensive. Being ongoing, labor cost rises with time. Machines can be bought for a fixed price, are reliable and faster, and can produce more in equivalent timeframes. As a result, dentists today enjoy lower costs for their lab prosthetics, while laboratories, due to higher volumes and fewer remakes, see better profitability despite the initial financial outlays for digitalization and CAD/CAM manufacture. Consistency is likely the greatest attribute of CAD/CAM technology, because "virtual design" for crowns, bridges, etc, enables assessment of the outcome before production occurs, and use of computer databases and artificial intelligence simplifies the technician's task of predicting morphology, occlusion, and dynamic function.

Monolithic Materials: The New Normal

The value of a master ceramist/technician cannot be overstated. On the other hand, skilled and experienced ceramists/technicians are in high demand if they can also work with CAD/CAM technology. Restorations in the esthetic zone and complex cases increasingly incorporate digital means, but the art and skill needed to duplicate human dentition in the mouth, especially in the anterior, is still beyond the capability of any machine today. Therefore, CAD/CAM-fabricated restorations still require varying levels of human intervention.

Dentists' preferred choices for posterior crowns are now primarily ceramic-based, displacing metal, with the most common materials being lithium disilicate and monolithic and layered zirconia.¹⁰ Monolithic restorations are more chip-resistant than layered ones because they lack weaker veneering porcelains and require fewer fabrication steps that potentiate chipping risk.

Lithium disilicate/silicate can be pressed (laboratory at higher cost) or milled (laboratory or chairside) with mid- to high-level esthetics for anterior and posterior applications and is very popular with chairside CAD/CAM dentists. Its clinical performance and durability are highly reliable for single units when following the manufacturer's recommendations for preparation and placement.^11,12

CAD/CAM monolithic zirconia is highly popular due to high ceramic strength and is advantageous for molar applications. It can be luted with conventional cements or adhesive resins and is economical and reasonably esthetic (tooth colored).^10,13 Also, it can be produced with chairside CAD/CAM. Original monolithic zirconia formulations are durable and reliable if properly processed and fabricated using laboratory data and practice-based studies.¹⁴ Conversely, they may be somewhat unesthetic due to high opacity and often are veneered to compensate. Higher-translucency monolithic zirconia materials are now available with an improved ability to blend with surrounding dentition. Their strength values are intermediate to those of lithium disilicate and original high-strength zirconia and, though promising, lack long-term clinical evidence.^12,15

Many laboratories can also produce CAD/CAM full- and partial-coverage restorations from materials other than zirconia and lithium disilicate using PMMA (long-term provisionals), composites, hybrid ceramics, glass-ceramics, and polycrystalline ceramics (zirconia). Alternatively, chairside systems offering same-day treatment may be more efficient and cost-effective for dentists interested in multiple material options. The learning curve is much shorter today, though adroit integration of acquired skills is essential for clinical and financial success, because chairside CAD/CAM's high cost demands adequate patient volume and a procedure mix that complements its capabilities.

Bridging the Divide: Digital Impressions

Early adopters circa 1985 to the early 1990s of chairside CAD/CAM were ahead of the digital curve compared to laboratories at the time. Now, however, although the growth of chairside CAD/CAM has been steady, digital CAD/CAM for laboratories is firmly entrenched. Chairside CAD/CAM is less of a laboratory competitor today than it was initially. Chairside systems now have the option of chairside production or electronic transmittal of the digital impression to the laboratory. Synergism rather than competition more appropriately describes the full embrace of digital CAD/CAM methods. Despite this, traditional impressions are still the primary means for providing laboratories the information needed to construct indirect restorations.

"Quality" elastomeric impressions should producequality results, assuming no errors in handling, an accurate working model, and fabrication with good craftsmanship.^13,16 Still, laboratories today consider impression quality problematic in terms of providing high-end results, and elastomeric impressions are rapidly becoming a broken cog in the gears of the dentist-lab workflows. A digital impression (DI) device or intraoral scanner replaces the elastomeric impression by obtaining the virtual working model directly from the mouth with no intermediate steps. Prosthetics derived from DI devices can equal or better those produced from elastomeric materials.^17,18

The scanned arch goes directly to production once it is received as a digital/electronic STL file from any such device. There is no gypsum stone, trimming, pinning, articulation, and so on. Ifneeded, models are 3D printed from the digital STL file in quantity with other cases rather than one at a time. Dentists have many options today for DI and chairside systems with DI now being the fastest-growing segment, costing less than full chairside systems, and possibly representing an ideal starting point. Lastly, dentistry is well beyond milling alone with 3D printing now common in laboratories and in the early stages of incorporation at digitally inclined dental practices. Additive process versus subtraction (milling) can efficiently manufacture models, appliances, temporaries, dentures, aligners, and patterns, with material-dependent restorations likely not too far off.

Conclusion

The value proposition has been established for chairside CAD/CAM manufacture in terms of workflow, convenience, and consistency. DI devices with or without chairside manufacture are now being developed and used for other applications. Many dentists are scanning allpatients as part of their secure dental record, improving diagnostics, monitoring conditions over time, and enhancing patient communications. For dentists not interested in chairside manufacture, costs may be more in line with ability to successfully amortize, but intraoral scanningsystems that allow for add-on capabilities later have the greatest advantage.

Much like camera film has given way to digital replication, digital technologies now affect the value proposition for dental services. Patients rightly expect medical/dental services to be planned for and made using digital imaging, virtual design, and precision manufacture-think "paper checks" (impressions) versus electronic transactions (digital impression files). The expense to equip and technologically maintain a dental office today exceeds that of the past, but the change is for the better and all businesses adjust. DI systems or intraoral scanners offer an affordable starting point for dentists to fully integrate with digital workflows, closing the digital divide with their lab. CAD/CAM manufacture is mainstream for dentistry and the "tipping point" has been reached.

About the Author

Daniel J. Poticny, DDS
Adjunct Clinical Associate Professor, Department of Cariology, Restorative Sciences, and Endodontics, University of Michigan School of Dentistry, Ann Arbor, Michigan; Private Practice, Grand Prairie, Texas