Aesthetic and Void-Free Cementation of Onlays

INTRODUCTION
When cementing an inlay or onlay, every dentist dreads seating the restoration only to find that cement oozes perfectly out of all but one section of the cavosurface margins. Many struggled with this issue in the days of hand-mixed cements and with the practice of “buttering” inlays and onlays for cementation. As dental professionals know, voids in the cement can lead to marginal leakage and recurrent decay and sensitivity, and it is imperative to observe that cement oozes from all aspects of the margins when seating the restoration. Fortunately, recent innovations in cement delivery have given dentists more options for reliable and void-free placement of inlays and onlays.
In addition to helping to prevent voids, a reliable cement should flow evenly onto the adhesive substrate without being sticky or stringy. However, it should be thixotropic enough to stay put where it is placed, without drifting into subgingival spaces or interproximal contacts. It should come in a variety of shades to match both the tooth and restoration.
Today, cements are more than just “space fillers,” as many contemporary indirect restorations require strong adhesion to the tooth substrate when conservative, least-invasive preparations are utilized. Conservative dentistry dictates that only the defective portion of the tooth is prepared, often negating the ability to create classical retention and resistance preparation forms utilized with more aggressive full and partial coverage crowns.

Figure 1. Failing amalgams on teeth Nos. 18 and 19.	Figure 2. Moderate recurrent decay was visible after removal of the old amalgams.
Figure 3. Shrink-wrap provisional.	Figure 4. The lithium disilicate (IPS e.max [Ivoclar Vivadent]) restoration shown on the model.
Figure 5. A porcelain primer (RelyX Ceramic Primer [3M ESPE]) was applied to the intaglio surface of the onlay.	Figure 6. Self-adhesive resin cement (RelyX Unicem 2 Automix Cement [3M ESPE]) was injected using a fine “mosquito” application tip into the internal aspects of the preparation.

The progression from metal-based prosthetic crowns, inlays, and onlays to contemporary all-ceramic alternatives has been mitigated by development of cement systems that either mechanically or chemically (or both) lute both the tooth substrate to restoration. The so-called “traditional” materials such as polycarboxylate and zinc phosphate cements, and the more contemporary and improved materials, such as glass ionomer and resin-reinforced glass ionomer cements, have been used successfully with full-coverage metal-based crowns with adequate retention and resistance form. However, these cements either lack the sufficient bond strength or possess negative physical properties that render them contraindicated for some modern all-ceramic restorative materials.
Self-adhesive resin cements, which entered the market about 10 years ago, have proven to be very popular with many clinicians. Dentists favor self-adhesive resin cements thanks to their strength, aesthetics, and ease-of-use; automix syringe delivery systems with a variety of delivery tip designs and sizes allow clinicians to place restorations more easily and predictably.
This class of self-adhesive cementation materials eliminates the need for etching, priming, and bonding by incorporating phosphoric acid modified methacrylate monomers. These monomers also aid in mechanical and dimensional stability by creating a cross-linked cement matrix during polymerization.¹ Data has supported the reliability of this class of material. A long-term study of one such cement, followed more than 1,450 all-ceramic and PFM restorations for 7 years after placement with a self-adhesive resin cement (RelyX Unicem 2 Automix Cement [3M ESPE]), demonstrated a debonding rate of just 2.4%; and postoperative sensitivity was found in only 1.1% of patients.² Clinical results have given additional backing to this cement, with studies showing its strong performance in areas including minimization of microleakage, sensitivity, and discoloration.^3-5
The following case demonstrates the use of a current self-adhesive cement to seat a lithium disilicate onlay on a first molar.

CASE REPORT
Diagnosis and Treatment Planning
A 32-year-old male presented with large, failing amalgams on teeth Nos. 18 and 19 (Figure 1). Due to the smaller size of the existing filling, a direct posterior composite was planned for No. 18. An indirect porcelain onlay was prescribed for No. 19 because the width of the previous amalgam was greater than two thirds of the intercuspal distance, and the functional distobuccal cusp replacement mandated the additional fracture resistance and flexural strength of an indirect porcelain material.

Clinical Protocol
Both teeth Nos. 18 and 19 were treated in the same visit. The patient was anesthetized and the existing amalgams were removed from the teeth, revealing moderate recurrent decay (Figure 2). The decay was removed and tooth No. 18 was restored with a direct occlusal posterior composite. A selective-etch technique was used (Scotchbond Universal Adhesive [3M ESPE]) and the tooth was restored with Filtek Supreme Ultra Universal Restorative (3M ESPE). Shade A2 Body was used to replace dentin and A2 Enamel to replace the enamel.
To treat tooth No. 19, the residual decay was first removed. The line angles were rounded and the walls were tapered to diverge occlusally to permit path of draw. A wash/tray vinyl polysiloxane (VPS) impression (Aquasil Ultra [DENSTPLY Caulk]) was taken and a temporary was fabricated using a bisacryl provisional material (Protemp Plus [3M ESPE]).

Figure 7. It is important to visualize excess cement flowing from all the cavosurface margins.	Figure 8. The restoration was tack-cured (Elipar S10 LED [3M ESPE]).
Figure 9. The excess was teased away from the margins with a sickle scaler.	Figure 10. Interproximal excess was removed with dental floss.
Figure 11. Prior to final finishing, glycerin was applied to all margins to prevent an oxygen-inhibited layer.	Figure 12. Definitive light-curing was done.

Figure 13. The final restoration. Note how well the cement matches both the tooth and restoration, leaving a seamless appearance.

The provisional was placed without the use of temporary cement via the “shrink-wrap” method. In this method, a preoperative dual-arch tray impression using the Gripper Tray (Discus Dental) is taken to be used as a matrix for temporary fabrication. The author utilized a VPS medium viscosity matrix material (Clear Bite [Discus Dental]) because it is fast and inexpensive, and it allows the clinician to see that it is properly seated while at the same time tasting good to the patient. After completion of the prep and impression, the area was disinfected and desensitized with a desensitizer (Gluma [Heraeus Kulzer]). The glutaraldehyde component is known to disinfect and cause the precipitation of plasma proteins in open dentinal tubules. Additionally, the hydroxyethyl methacrylate in Gluma is an ambiphilic primer that assists in the “wetting” of the bis-acryl provisional material. Because no provisional cement is used in this technique, this step is essential to assure an intimate seal that will eliminate sensitivity to temperature during provisional wear.
The assistant loaded the tray with the bis-acryl temporization material in shade A2, and the patient was instructed to bite into the dual-arch tray. The tray was allowed to set for approximately 2 minutes, and then removed. The provisional was retained in the preparation by excess acrylic flowing into interproximal undercuts. In the rare event that excess material goes deep under the gumline (causing a periodontal hazard), the clinician can adjust the temporary. The occlusion is typically perfect, but minor adjustments can be accomplished with an abrasive cup or point (Enhance [DENTSPLY Caulk]). The shrink-wrap provisional is shown in Figure 3, along with the completed Filtek Supreme Ultra restorative direct composite on No. 18. This technique can also be utilized for crowns and veneers.

Delivery Appointment for the Onlay
Two weeks following the temporization appointment, the patient returned to the office for placement of the final onlay. A pressed lithium disilicate material (IPS e.max [Ivoclar Vivadent]) was chosen as the restorative material because of its high flexural strength6 and precision fit (Figure 4).
The area was anesthetized and a rubber dam (Hygienic Framed Non-Latex Flexi-Dam [Coltène] was placed. (It is the clinician’s preference to seat inlays and onlays under rubber dam isolation, particularly in the mandible.) A “split dam” technique was used in this case; holes were punched for teeth Nos. 18 and 20, and then connected by a single scissor cut. There was no way to floss between the interproximal of the shrink-wrapped provisional on tooth No. 19, as the acrylic flowed into interproximal undercuts. Shrink-wrapped provisionals can be removed either with a spoon excavator, or by sectioning with a flame-shaped composite finishing bur (FSD3F [Komet USA]). These burs have “safe tips” which are noncutting and do not alter the preparation during this process.
The restoration was tried-in dry, and once the proper fit was confirmed, the cementation process was begun. The restoration was already etched with hydrofluoric acid by the dental laboratory team prior to shipping. After the onlay was tried in, it was cleaned with acetone. (No additional etching was done in the office.) Because lithium disilicate has a glass phase, it can be silanated to create silica-silane-resin bonding. Figure 5 shows a porcelain primer (RelyX Ceramic Primer [3M ESPE]) being applied to the intaglio surface of the onlay restoration. After application of the primer, it was air-dried.
RelyX Unicem 2 Automix Cement in shade A2 was chosen in this case to cement the onlay. Use of an automix syringe delivery system can save treatment time with easier handling and flexible dose dispensing. In addition, this kit contains a variety of mixing tips, offering different designs, which can be used according to the clinician’s preference and clinical situation. This author has personally found the thin “mosquito” endo tip particularly useful for inlay and onlay cases. Its delicate tip permits precise application to the margins, cavosurface, and the base of the preparation (Figure 6). Once the cement was applied to the onlay and seated, careful attention was paid to ensure that excess cement oozed from all aspects of the margins (Figure 7).
Once the restoration was seated, it was tack-cured with a curing light (Elipar S10 LED [3M ESPE]) for 3 seconds (Figure 8). This initiates early polymerization of the exposed marginal cement to a “dough state.” Next, the excess resin cement was teased away from the margins with a sickle scaler (Figure 9), and then the excess resin cement in the interproximal area was removed with dental floss (Figure 10). Prior to final light-curing, the margins were coated with glycerin (DeOX [Ultradent Products]) to permit the full curing of marginal cement without a residual air-inhibited layer (Figure 11). Figure 12 shows the final light-cure for one minute per surface.
The occlusion was adjusted with fine diamonds and polished with silicone points and cups. Figure 13 shows the definitive lithium disilicate restoration blending seamlessly with the resin cement and the natural tooth.

IN SUMMARY
The self-adhesive cement used in this case resulted in an excellent aesthetic match between the tooth and the onlay, while at the same time offering a strong bond and reduced postoperative tooth sensitivity.
As demonstrated in this clinical case, the endo tip of the syringe enabled precise application of the resin cement into the prepared tooth and onto the surface of the restoration. The risk for voids in the cement was greatly reduced by the flowable nature of the resin cement and the “mosquito” tip’s ability to make it easy to ensure the entire surface of the restoration is coated in cement.
Modern cementation materials and delivery systems make it possible to fulfill a patient’s desire for a highly aesthetic restoration that will be strong and worry-free for years to come.

References

1. 3M ESPE. RelyX Unicem—Self-Adhesive Universal Resin Cement in the Clicker Dispenser [technical data sheet]. multimedia.3m.com/mws/mediawebserver?mwsId=66666UF6EVsSyXTtmXfylxfcEVtQEVs6EVs6EVs6E666666&fn=uni_clicker_tech_data.pdf. Accessed June 4, 2012.
2. 3M ESPE RelyX Unicem Self-Adhesive Universal Resin Cement (7-year clinical performance). The Dental Advisor. 2010;27. Available at dentaladvisor.com/clinical-evaluations/evaluations/3m-espe-relyx-unicem-self-adhesive-resin-cement-7-yr.shtml. Accessed on August 28, 2012.
3. Behr M, Rosentritt M, Wimmer J, et al. Self-adhesive resin cement versus zinc phosphate luting material: a prospective clinical trial begun 2003. Dent Mater. 2009;25:601-604.
4. Geraldeli S, Stanford C, Dawson D, et al. Single and multi-step luting agents after four years. Paper presented at: IADR General Session; April 3, 2009; Miami, FL. Abstract 1639.
5. Peumans M, De Munck J, Van Landuyt K, et al. Two-year clinical evaluation of a self-adhesive luting agent for ceramic inlays. J Adhes Dent. 2010;12:151-161.
6. Ivoclar Vivadent. IPS e.max Flexural Strength. ivoclarvivadent.us/emaxchangeseverything/lithium-disilicate/flexural-strength.php. Accessed June 4, 2012.

Dr. Blank maintains a private practice in Rock Hill, SC, where he emphasizes comprehensive restorative and cosmetic reconstruction. Dr. Blank is an adjunct professor of general dentistry at the Medical University of South Carolina, and a guest lecturer for graduate and undergraduate studies. He has consulted with dental manufacturers and lectured throughout the United States on the recent advances in adhesion technology and the benefits of various cosmetic techniques. He can be reached at (803) 327-3240 or at carolinasmilecenter.com.

Disclosure: Dr. Blank received a small stipend from 3M ESPE for writing this article.