The Evolution Of Posterior Aesthetics

by Stephen Poss, DDS

In most publications the excitement and interest seems to revolve around anterior aesthetics. Which anterior material and technique seems to look the best and last the longest? With so much focus on veneers and other anterior aesthetics, sometimes the posterior aspect of the mouth seems to be overlooked. In reality, posterior restorations are the “bread and butter” of most dental practices, especially with the economy as uncertain as it is today.

One restorative aspect is direct composites, which are continuing to evolve. The microhybrids are incorporating more and more nano-technology and increasing the strength and polish over composites developed just a few years ago. Larger class II composites can be placed with less shrinkage and more strength (Figs. 1 & 2). The main concern of these types of restorations is depth of cure and porosity. This clinician would still recommend layering deep composites 2-3mm at a time. Posterior composites still have certain limitations. This is especially true when replacing a missing cusp or fracture in the tooth.

Along with direct composites, adhesive dentistry has evolved dramatically in the last several years. Even though total-etch is still the recommended technique by most clinicians, the self-etching market is continuing to become more accepted as the self-etch adhesives continue to improve.

There seems to be a difficult transition for dentists when a direct restoration is not adequate. Most clinicians seem to proceed to a full coverage crown.

In posterior restorative needs, porcelain fused to metal is still utilized in most cases that require strength and ease of use. Because the preparation design is very forgiving, a feather margin or a butt joint seem to be effective clinically. One of the concerns with porcelain fused to metal restorations is hiding the margins for aesthetic reasons. This usually means that the margins are placed subgingivally. As new metal-free materials have become available, patient demand is allowing the dentist to make other choices for crowns as well as bridgework.

Though there is a long clinical history of adhesive porcelain and resin inlays and onlays, most dentists opt for full coverage.

This clinician prefers laboratory processed resin inlay/onlays, especially when replacing one cusp or less. BelleGlass (Kerr Lab), Cristobol (Dentsply Prosthetics), and Gradia (Hereaus) are among a few that have outstanding physical properties. These indirect resins, especially BelleGlass, have over 15 years of clinical history (Figs. 3 & 4). This clinician utilizes almost 50% of posterior laboratory restorations as inlay/onlays. The dentist often is able to conserve more tooth structure and preserve the gingival health. As for aesthetic concerns, laboratory fabricated resins is one of those restorations that truly has chameleon properties of becoming virtually undetectable once they are placed.

Depending on the clinician’s preference, pressed ceramics can also be utilized as inlays/onlays. The compressive strength of pressed ceramics is slightly higher than laboratory processed resin. This would include products like Empress (Ivoclar Vivadent) and Finesse (Dentsply Prosthetics). Pressed ceramics has also shown to be relatively kind to the opposing dentition when it comes to wear (Figs. 5 & 6).

Pressed ceramics has also been the choice of many clinicians’ for single crowns and veneers. However, pressed ceramic placement in the molar area is less predictable and contraindicated for bridgework.

Alumina (Procera) had an increase in compressive strength compared to most pressed ceramics with almost 600 MPa. This strength allowed more traditional cementation techniques to be used. Some clinicians expressed concern about fit and esthetics. Consequently, with new advances in the ceramic market today alumina is utilized less.

Ivoclar Vivadent has released E-Max. This is a lithium disilicate. The flexural strength is almost twice that of IPS Empress at around 400mpa. This material is indicated for veneers, inlays, onlays, anterior and posterior full coverage crowns and limited bridgework replacing premolars and anterior teeth. The recent release of the translucent ingot has made this material very well received, resulting in dental laboratories blending E-Max to most other dental materials, if used correctly (Figs. 7 & 8).

Zirconia, the strongest metal-free dental material available, has evolved over the past decade to be a viable choice. Zirconia products like Cercon (Dentsply Prosthetics) and Lava (3M ESPE) have made great strides to make this material more aesthetic. Improvements with fit and contour are due to advancements in CAD/CAM technology. The framework for Zirconia has a flexural strength above 900MPa. In addition, various layering porcelains can be placed over the Zirconia. The indications are for crowns and bridgework and have the capability for full arch placement with the proper abutment design (Fig. 9).

The main concerns with Zirconia are two fold. The first is the clinician has to be more aggressive with their preparation, requiring almost 1mm reduction facially as compared to .4-.6mm for pressed ceramics. The other main concern is Zirconia-based products cannot be internally etched. As such, in some clinical situations the internal aspects of the Zirconia will not adhere to the resin cement adequately. With porcelain, whether they are Feldspathic or pressed ceramics, the internal aspects can be etched with hydrof louric acid and silinated to create a sound micro-mechanical attachment to the resin cement.

Advancements in digital technology have contributed to great improvements with in office laboratory systems such as Cerec 3D and E4D. These systems can benefit the clinician in the respect that the patient can have their laboratory crown in one appointment with no impressions and no provisionals. The learning curve for the dentist can be difficult, as well there is large capital investment required to introduce this modality into your practice. However, without a doubt, this technology is surely to be part of the future of dentistry (Figs. 10 & 11).

The ever changing and improving technology of dental materials has made dentistry much more aesthetic as well as easier to use than before. The options in adhesive dentistry and the materials available make this an exciting era in dental history.

Acknowledgement

The author would like to thank Dr. Chris Pescatore for the outstanding dentistry illustrating Cerec 3D crown fabrication (Figs. 10 & 11).

Dr. Poss lectures internationally on esthetic dentistry and TMD. He is an active consultant to several dental manufacturers in the area of new product development and refinement. He maintains a cosmetic oriented restorative practice in Brentwood, Tennessee. He can be reached at:Beautifulsmiles@earthlink.net

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The main concern of these types of restorations is depth of cure and porosity

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The compressive strength of pressed ceramics is slightly higher than laboratory processed resin

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The other main concern is Zirconia-based products cannot be internally etched

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