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Delivering Optimal Results for

Fixed Partial Dentures

Chris Salierno, DDS and

David R. Avery, AAS, CDT

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DENTAL LEARNINGDelivering Optimal Results forFixed Partial Dentures

EDUCATIONAL OBJECTIVES

The overall goal of this article is to provide the reader with infor-mation on current materials and techniques for the fabrication of a fi xed partial denture (FPD). After reading this article, the reader will be able to:1. List in detail the steps involved in fabrication of an FPD;2. Describe the impression materials available, considerations in

their selection, and the use of a one-stage or two-stage technique;3. Review the materials and techniques available for the fabrication

of provisional restorations; and4. List and review the steps involved in the fabrication of full-

contour zirconia CAD/CAM restorations.

Fixed partial dentures require careful consideration of the materials and treatment protocol that will be followed. The successful recording of preparations, manufacture of multi-unit restorations, and their delivery intraorally is aided by astute attention to material properties at each of these critical stages. Detailed communication and collaboration with the laboratory are also required to ensure clinical success and the best possible outcomes.

ABOUT THE AUTHORS

Chris Salierno, DDS, received his BS from Muhlenberg College and his DDS from SUNY Stony Brook School of Dental Medicine. He completed his formal training at Stony Brook Hospital’s General Practice Residency program where he focused on implant prosthetics. While in dental school, he was the National President of the American Student Dental Association. Today, he continues his advocacy efforts with the New York State Dental Association and Suffolk County Dental Society. Dr. Salierno lectures on his particular areas of interest, including occlusion, dental materials, prosthodontics, and implant prosthodontics. He enjoys helping audiences integrate the latest research into everyday practice. In 2005, he returned to his former dental school as an Assistant Clinical Profes-sor. AUTHOR DISCLO SURE: Dr. Salierno does not have a leadership position or a commercial interest with

DENTSPLY Caulk or DENTSPLY Prosthetics, the commercial supporters of this course or with products and services discussed in this educational activity. Dr. Salierno may be reached at [email protected]

David Avery, CDT, actively teaches undergraduate and post-graduate dental students at the University of North Carolina, Medical University of South Carolina, Medical College of Georgia, Virginia Commonwealth University, University of Tennessee, University of Mississippi, Tufts University and University of West Vir-ginia dental schools. He is also a visiting lecturer at the Carolina’s Medical Center, Wake Forest University, University of Virginia Hospital, University of Florida, and the McGuire Veterans Administration Hospital in Richmond, Va., as well as numerous residency programs within the US Armed Forces. He has published in numerous laboratory and clinical journals and has presented more than 600 scientifi c programs. He is a board member of the Dental Technician Alliance of The American College of Prosthodontists. Mr. Avery received his

AAS degree in dental laboratory technology from Durham Technical College in Durham, North Carolina in 1976 and achieved his Certifi ed Dental Technician status in 1980. AUTHOR DISCLO SURE: Mr. Avery is a speaker for DENTSPLY International. Mr. Avery may be reached at [email protected]

ABSTRACT

SPONSOR/PROVIDER: This is a Dental Learning, LLC continuing education activity. COMMERCIAL SUPPORTER: This course has been made possible through an unrestricted educational grant from Dentsply Caulk. DESIGNATION STATEMENTS: Dental Learning, LLC is an ADA CERP recognized provider. ADA CERP is a service of the American Dental Association to assist dental professionals in identifying quality providers of continuing dental education. ADA CERP does not approve or endorse individual courses or instructors, nor does it imply acceptance of credit hours by boards of dentistry. Dental Learning LLC designates this activity for 2 CE credits. Dental Learning is also designated as an Approved PACE Program Provider by the Academy of General Dentistry. The formal continuing education programs of this program provider are accepted by AGD for Fellowship, Mastership, and membership maintenance credit. Approval does not imply acceptance by a state or provincial board of dentistry or AGD endorsement. The current term of approval extends from 2/1/2016 - 1/31/2020. Provider ID: # 346890 Dental Learning, LLC is a Dental Board of California CE provider. The California Provider number is RP5062. This course meets the Dental Board of California’s requirements for 2 units of continuing education. EDUCATIONAL METHODS: This course is a self-instructional journal and web activity. Information shared in this course is based on current information and evidence. REGISTRATION: The cost of this CE course is $29.00 for 2 CE credits. ORIGINAL RELEASE DATE: September, 2012. REVIEW DATE: August, 2015. EXPIRATION DATE: July, 2018. REQUIREMENTS FOR SUCCESSFUL COMPLETION: To obtain 2 CE credits for this educational activity, participants must pay the required fee, review the material, complete the course evaluation and obtain a score of at least 70%. AUTHENTICITY STATEMENT: The images in this course have not been altered. SCIENTIFIC INTEGRITY STATEMENT: Information shared in this continuing education activity is developed from clinical research and represents the most current information available from evidenced-based dentistry. KNOWN BENEFITS AND LIMITATIONS: Information in this continuing education activity is derived from data and information obtained from the reference section. EDUCATIONAL DISCLAIMER: Completing a single continuing education course does not provide enough information to result in the participant being an expert in the fi eld related to the course topic. It is a combination of many educational courses and clinical experience that allows the participant to develop skills and expertise. PROVIDER DISCLOSURE: Dental Learning does not have a leadership position or a commercial interest in any products that are mentioned in this article. No manufacturer or third party has had any input into the development of course content. CE PLANNER DISCLOSURE: The planner of this course, Casey Warner, does not have a leadership or commercial interest in any products or services discussed in this educational activity. She can be reached at [email protected]. TARGET AUDIENCE: This course was written for dentists, dental hygienists, and assistants, from novice to skilled. CANCELLATION/REFUND POLICY: Any participant who is not 100% satisfi ed with this course can request a full refund by contacting Dental Learning, LLC, in writing. Please direct all questions pertaining to Dental Learning, LLC or the administration of this course to [email protected]. Go Green, Go Online to www.dentallearning.net take your course. © 2015

CE EditorFIONA M. COLLINS

Managing EditorBRIAN DONAHUE

Creative DirectorMICHAEL HUBERT

Art DirectorMICHAEL MOLFETTO

Copyright 2015 by Dental Learning, LLC. No part of this publication may be repro-duced or transmitted in any form without prewritten permission from the publisher.

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DENTAL LEARNING

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Introduction

An FPD remains a viable treatment option for patients who elect to replace missing teeth without receiving implants. Advances in impression materials, cements,

and provisional and definitive restorations have expanded the options for clinicians to select a protocol that suits their preferences. These advances have, however, also increased the potential for operator and laboratory error. Techniques and materials may not be interchangeable without consequences, depending on the materials, and clinicians must be astute in their cultivation of a protocol and must work in concert with the laboratory to deliver a predictable restoration for their patients. The first step is pre-operative diagnostics, followed by the clinical and laboratory steps required to deliver the FPD. The value of a diagnostic wax-up in planning fixed re-storative procedures is well-documented.1,2 Excellent commu-nication and collaboration with the laboratory is important. Following preparation of the abutment teeth, subsequent clinical steps include soft tissue management, the use of a custom tray for the final impression, provisionalization and luting of the final FPD. Each of these is important for the final result and the clinical success of the FPD.

Soft Tissue Management and Impression TakingThe prepared abutment teeth are surrounded by interfer-

ences that can prevent their accurate reproduction. Isola-tion of the areas of interest is primarily concerned with the displacement of the gingiva from the prepared margins of the abutment teeth, which may be achieved through the use of retraction cord, a compressive cap, or expanding pastes. Surgical displacement may be accomplished through meth-ods that include the use of a scalpel, electrosurgery, or a soft tissue laser. Other adjacent structures, such as buccal mucosa and the tongue, can be relocated with cotton rolls, gauze, and saliva evacuator systems. Remaining moisture around the prepared abutment teeth, such as gingival crevicular fluid and blood, can be reduced by the application of ferric sulfate, epinephrine, and other chemical means.

For a traditional impression, a tray is selected to fit the arch. Double-arch trays or “triple trays” are convention-ally indicated for one to two units in the same arch when a

stable, reproducible occlusion is present.3,4 A full-arch tray is selected for bridges to give the laboratory technician more information to correctly articulate models and create an ac-curate plane of occlusion. An impression for an FPD is more predictably made in a custom tray than a stock tray.5 A cus-tom tray made from a cured resin is more closely adapted to the arch than a stock tray and thus requires a smaller, more uniform amount of impression material.6 There are several steps occurring in a short period of time during impression taking that require the clinician’s vigilance. A custom tray re-lieves the burden of ensuring that the tray has been correctly seated to capture the entire arch. A contemporary method of custom tray fabrication utilizes a visible-light-cured (VLC) custom tray material. The ability to adapt the pliable material in an uncured state, and to cut back borders prior to curing, minimizes the finishing time required. The curing shrinkage is minimal, ensuring a well-adapted result.

Impression MaterialsElastic impression materials should demonstrate excel-

lent dimensional stability, have an adequate working time, short setting time, and be easy to use with sufficient flowability. The requirements for impression materials are addressed by the American National Standards Institute in collaboration with the American Dental Association.7 Polyvinylsiloxane and polyether impression materials are common choices for indirect restorative procedures. Their dimensional stability permits time for transportation to a dental laboratory, and both materials are suitable for mul-tiple pours without clinically significant loss of accuracy.8 For restorations with larger numbers of units, a longer working time is required and can be achieved by cooling the impression material in the fridge prior to use. Alter-natively, an impression material with extra working time should be selected. The clinician’s selection rests upon his/her comfort with the material’s properties (Table 1).

Impression TechniquesImpressions for indirect restorations follow either a

one-step or two-step protocol. The one-step technique cap-tures gross and fine detail at the same time. Both polyether

Delivering Optimal Results for Fixed Partial Dentures

5August 2015

and polyvinylsiloxane impression materials are available in different viscosities for greater clinician control. The clini-cian may use a single viscosity impression material, typi-cally of a medium consistency, for both the tray and tooth detail. The advantage to this approach is that using only one material eliminates concerns of a poor mixture of vis-cosities. Alternatively, the clinician may use two different viscosities: typically, a heavier body or silicone putty for the tray and a lighter body for tooth detail. If the manu-facturer’s instructions for working and setting times for both materials are followed, distortions such as pulls and inconsistent mixtures should be eliminated. Note however that an increase in room temperature reduces the working time for impression materials. The advantage gained is the ability of a lighter body material to flow into smaller areas for greater detail, aided by the compressive strength of the surrounding heavier body material. Alternatively, the two-step technique first captures gross detail with silicone putty in the tray. Typically, a thin film spacer is placed over the teeth to leave room for impression material in the second step. Next, the finer tooth detail is captured with a lighter body impression material.

Provisional FabricationA successful provisional restoration for an FPD must

protect the prepared abutment teeth and gingiva, maintain the three-dimensional relationship between the abutment teeth and the opposing dentition, and maintain function

and esthetics.9 These objectives are similar for single-unit provisional restorations; however, strength, rigidity, and ease of use become more critical for multi-unit restora-tions (Table 2). It is a challenge to fabricate a provisional restoration efficiently while the patient is in the operatory and yet still ensure that all of the parameters for success are met. Fortunately, modern clinicians have a variety of materials and techniques at their disposal to cultivate a procedure that is the most predictable in their hands. Op-tions include chairside and laboratory fabricated provi-sional FPDs in a variety of materials.

A provisional FPD is intended to last for the duration of time required to fabricate the final restoration. The clinician may also elect to have the patient wear the provi-sional for an additional “trial” period before final impres-sions are made to evaluate esthetics or occlusal stability, and/or to allow time for soft tissue healing.

Provisional MaterialsThe three most prevalent materials used for a provisional

FPD are methyl methacrylate, ethyl methacrylate, and bis-acryl composite resin. Methyl methacrylate has the longest track record in dentistry and is still widely used. A powder and liquid are mixed together to initiate the setting reaction. Despite its good strength and longevity when set, methyl methacrylate is known to be problematic during the setting

Table 1. Comparison of common fixed partial denture impression materials

Polyvinylsiloxane Polyether

Excellent dimensional stability Excellent dimensional stability

Hydrophobic Hydrophilic

Easy removal after setting More difficult removal after setting

Fair odor and taste Poor odor and taste

Setting inhibited by latex Setting unaffected by latex

Can be stored wet or dry Must be stored dry

Table 2. Optimal properties for provisional bridge restorations

Property of Material Clinical Purpose

Ease of fabrication Reduced chair time

Ability to be relined Ensure marginal fit

Flexural and compressive strength

Resistant to fracture or distortion

Rigidity Maintain abutment relationship

Biocompatibility Non-irritating to pulp or gingiva

Ability to be polished Resistant to plaque accumulation

Color stability Patient acceptance

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reaction. The reaction generates significant heat, which may damage the pulp and gingival tissues.10 Also, the material shrinks while curing, which may lead to poor marginal fit.10 If the provisional is removed from the abutment teeth while setting and is not quickly reinserted, the shrinkage of the material may distort the provisional’s internal aspects so that it no longer may be seated on the abutment teeth. Concerns have also been raised that pulpal and gingival irritation can result from the presence of free monomer.11 Differences also exist between different versions of the same chemical material.12 Ethyl methacrylate is also a powder and liquid mixture but offers better marginal integrity and less heat generation during setting than methyl methacry-late. However, these advantages are offset by the poor color stability and difficulty of use.13 Methyl methacrylate and ethyl methacrylate acrylic resins may be used chairside using the direct technique whereby the material sets via self-cure or autopolymerization. When an indirect technique is used in the laboratory, both acrylic resins may be heat-processed for additional strength and color stability (Table 3).14

Recently, bis-acryl composite resin has emerged as a popular choice for fabrication of a crown and bridge provisionals. Available in self-mixing cartridges, bis-acryl exhibits good marginal fit and low heat generation dur-ing setting.15 Advantages include less heat generation and shrinkage during polymerization than the methacrylate acrylic resins. One study showed shrinkage of bis-acryl resin to be up to 1.7% by volume compared to 6% for methyl methacrylate.16 As a composite resin, bis-acryl

material is compatible with bonding materials used for operative dentistry. Small areas of the provisional in need of repair or reline may be reliably restored with flow-able composite resin, which decreases chair time without sacrificing predictability. Bis-acryl resins may be self-cure, light-cure, or dual-cure, depending upon the clinician’s preference. A notable disadvantage of the material is its decreased strength compared to acrylic resins over time.17 However, indirect fabrication of a bis-acryl composite resin provisional by a laboratory will improve its strength.18

The most recent material development in the provi-sional resin category is a unique visible-light-cured hybrid resin technology. This material provides for excellent wear rates as well as low solubility and resistance to staining and color change, and is cleared by the FDA for three years of clinical use.19 The “wax-like” handling character-istics of this resin provide the technician with a familiar, easily adaptable technique that can be utilized to produce extremely accurate provisional restorations. The low wear rate and strength are particularly important for long-term provisional restorations.19

Provisional CementationRetention of a provisional restoration is commonly

relegated to the weaker cements such as zinc oxide euge-nol and zinc oxide non-eugenol, to aid removal when the permanent restoration is ready for placement. Eugenol is respected for its bactericidal properties, which can aid in reducing post-operative sensitivity.20 However, it also acts

Table 3. Comparison of acrylic and composite resin materials for provisional fabrication

Methyl methacrylate - Advantages Methyl methacrylate - Disadvantages

Longer term strengthMost significant curing exothermiaMost significant curing shrinkage

Ethyl methacrylate - Advantages Ethyl methacrylate - Disadvantages

Longer term strength Poor color stability

Bis-acryl composite resin - Advantages Bis-acryl composite resin - Disadvantages

Ease of use and repairLeast significant curing exothermiaLeast significant curing shrinkage

Shorter term strengthExpense


7August 2015

as a plasticizer, detrimentally affecting the polymeriza-tion of acrylic and composite resin.21 Thus, a provisional that has been previously luted with a eugenol-containing temporary cement will be difficult to reline or repair. The added material will be softer than normal and could po-tentially unsuccessfully adhere to the original provisional. In addition, eugenol could negatively affect the polym-erization of a permanent resin cement. As resin cements grow in popularity, many clinicians prefer to select a tem-porary cement that does not contain eugenol to avoid such complications. Zinc oxide non-eugenol cements substitute organic acids in place of eugenol, which actually makes the cements stronger.22 If an FPD provisional is expected to be retained for a long period of time, or if additional reten-tion is required, a stronger cement such as zinc polycar-boxylate is often substituted.

Restoration InsertionSuccessful luting of the final restoration begins with

successful debridement of the abutment teeth. After the provisional restoration is removed, debris and provisional cement remnants are removed to ensure proper definitive cementation. Some clinicians elect to mechanically debride the surfaces with an explorer, an air/water syringe spray, polish with pumice slurry, and/or scale with ultrasonic instruments. Other clinicians use chemicals such as a dis-infecting agent to decrease post-operative sensitivity23 and/or a cleansing agent to remove the smear layer and expose dentin tubules for improved resin cement bonding.24

Restoration AdjustmentWhen trying in the final prosthesis it may be necessary

to reshape the occlusal and interproximal porcelain to achieve harmony with the rest of the dentition. Adjust-ments with a diamond bur introduce irregularities to the otherwise smooth, glazed porcelain surface. Remaining surface roughness may be treated with a series of extra-oral or intra-oral polishers to achieve the same smoothness as a glaze finish.25 A smooth finish is desirable because rough porcelain may injure the opposing dentition26 and accumulate plaque.27 Special attention must be paid to

ceramic restorations fabricated from zirconia. Due to its unique tetragonal, polycrystalline structure, zirconia increases its volume around a stress-induced crack. This phenomenon, known as transformation toughening, contributes to the material’s high flexural strength of up to 1,200 MPa.28 Although some studies have concluded that adjusting zirconia can actually increase its strength,29 other studies have pointed out that significant pressure and use of coarse diamonds can introduce cracks beneath the sur-face and actually weaken the zirconia.30 To avoid introduc-ing a critical crack, a light touch with fine diamond burs under copious air/water spray is advised when adjusting zirconia.30 If the fitting of a zirconia core or full-contour zirconia bridge would require that the intaglio surface be adjusted for proper seating, it is recommended that the abutment tooth be adjusted instead.31 This is due to the difficulty of polisher systems in accessing the internal aspects of a restoration.

Definitive luting agents are selected based upon the condition of the abutment teeth and the restorative material used for the prosthesis. Traditional dental cements such as zinc phosphate and zinc polycarboxylate are mechanically retentive by flowing into the discrepancy between tooth and restoration and hardening. This hardening is due to an ionic reaction and is therefore soluble in the oral environment over time.32 Resin cements are retentive by serving as an ad-hesive medium between the tooth and the restoration. Ideally suited for all-ceramic restorations, which may be capable of being etched and bonded, resin cements are also used with metal-ceramic restorations due to their low solubility.

The resin cement bond to the ceramic restoration is dependent on the nature of the restorative material. Ceram-ics that contain glass, such as feldspar and lithium disilicate, may be predictably etched with hydrofluoric acid. Subsequent treatment of the etched surface with a silane coupling agent will prepare the glass ceramic for bonding to a resin cement.33 Zirconia’s polycrystalline structure does not contain glass and therefore cannot form a bond to the resin cement that is as predictable or as strong as a glass ceramic, despite vari-ous methods of surface conditioning.34 The manufacturer’s instructions for a given material must be followed.

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The resin cement bond to the abutment teeth is achieved using either a total-etch, self-etch, or self-adhesive protocol. The total-etch technique begins with chemical re-moval of the smear layer and hydroxyapatite crystals. The etch is washed off and a hydrophilic primer and unfilled bonding resin are applied, which penetrate the exposed enamel and dentin structures to form a hybrid layer. The tooth surfaces with exposed hybrid layers are now able to adhere to the resin cement. Self-etch systems do not com-pletely remove the smear layer and do not penetrate into the tooth structure as deeply. The bond is not as strong as the total-etch technique but there is also a decreased chance of post-operative sensitivity.35 Self-adhesive systems incorporate the etch, prime, and bonding elements into the resin cement itself. These offer the weakest bond of the resin cement family but are the easiest to use clini-cally.36 Self-adhesive cements are not recommended for preparations with insufficient resistance form due to their poorer bond strengths. However, the overall surface area of multiple, prepared abutments for an FPD will generally offer sufficient resistance form for a self-adhesive cement to be used.

Resin cements are also classified as self-cured, light-cured, or dual-cured. Light-cure cements are most predict-able when a translucent ceramic restoration is less than 1.5 mm thick.37 When the thickness of the translucent ceramic

restoration is greater than 2.5 mm, penetration of a curing light is unpredictable. In these cases, and for restorations that do not transmit light, a self-cure or dual-cure resin cement is recommended. A final category of luting agent for use with FPD restorations is glass-ionomer and resin-modified glass ionomer cements. A notable advantage with this material is the cariostatic release of fluoride from the cement to the abutment tooth.38 However, the material is known to expand after cementation, which limits its use to metal-ceramic and zirconia ceramic restorations.28

Case StudyA 51-year-old male, who was a new patient with no

relevant medical history, presented for replacement of a fractured porcelain-fused-to-metal FPD spanning teeth #29 to 31 (Fig. 2). His dental history was significant for brux-ism, as was evidenced by the generalized moderate wear facets on the dentition. The existing FPD demonstrated considerable fracturing of porcelain and destruction of the metal substructure. Tooth #31 had a prior history of endodontic therapy that had required access through the occlusal surface of the FPD. This access had been sealed with a composite resin that now showed signs of marginal leakage and may also have contributed to the fracturing of the occlusal porcelain (Fig. 3). The patient was treatment planned for a full-contour zirconia bridge to prevent future

Figure 1. Resin cement bonding protocols Figure 2. Preoperative appearance of FPD #29-31, buccal and occlusal views. Note that the dentition in the same quadrant is A3 while the opposing dentition is more A2


9August 2015

porcelain fracture associated with his bruxism habit. Pre-liminary impressions and a bite registration were sent to the laboratory for the development of a wax-up. The FPD would be stained to incorporate the shade of the adjacent teeth in the same quadrant (A3) and the opposing denti-tion (A2).

At the treatment visit, while waiting for adequate anesthesia, a pre-operative impression was taken using a polydimethylsiloxane impression in a stock tray. This impression was set aside for later use during fabrication of the provisional bridge. The original bridge was carefully sectioned and removed so as to preserve remaining tooth structure. The composite resin filling the endodontic access on tooth #31 was removed and the remaining four walls of tooth structure were etched, bonded, and filled with a

dual-cure, fluoride-releasing core buildup material. The preparations were completed with supragingival margins to aid hygiene, although had the tooth margins appeared in the esthetic zone, the margins would have been prepared equi-gingivally.

A custom tray was fabricated using light-cured materi-al, for use during taking of the final impression to improve its accuracy (Fig. 4). A polyvinylsiloxane material was selected as adequate isolation and moisture control had been achieved. Application of a surfactant was performed to optimize flow of the impression material over the tooth surfaces and around preparation margins. A heavy body polyvinylsiloxane impression material was mixed into the custom tray while a light body polyvinylsiloxane impres-sion material was loaded into a metal syringe. The cord

Figure 4. A custom tray with occlusal stops allows for an even thickness of impression material to capture necessary detail

Figure 5. Clear margins with flash in the gingival sulcus

Figure 3. Above: Abutment teeth after bridge removal. Below: The composite resin buildup was replaced by a dual-cure core buildup material. Note the slightly supragingival margins left for hygiene access

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was removed and the light body material was syringed into the sulcus, one prepared abutment at a time. After all surfaces of interest were covered, an air syringe was gently used to thin the impression material to reduce polymeriza-tion shrinkage. The full-arch tray of heavy body material was easily seated because it had been customized for the patient. After the setting time of five minutes had expired, the tray and impression material were removed and in-spected for accuracy. The margins were shown to be fully captured with additional light body material well into the gingival sulcus (Fig. 5). The opposing arch was recorded with a polydimethylsiloxane impression material in a stock tray. This material demonstrates good dimensional stability and does not have to be poured in stone before transporta-tion to the dental laboratory. An interocclusal record was

recorded using rigid fast-set polyvinylsiloxane. This form of polyvinylsiloxane offers less resistance to biting forces and sets more quickly, reducing the chances for jaw move-ments to alter the record.

A provisional bridge was fabricated by dispensing a bis-acryl resin into the pre-operative impression (Fig. 6). The tray was reseated intraorally and allowed to cure for 90 seconds. After removal, a curing light was held over the pro-visional bridge for 20 seconds to expedite the curing process (Fig. 7). This step aids in removal of the provisional bridge from the pre-operative impression while avoiding distortion or fracture. The provisional bridge was trimmed with a thin flame diamond bur and checked intraorally for marginal integrity and occlusal harmony. An advantage of bis-acryl resin is its ability to easily bond with composite resin.

Figure 6. Bis-acryl provisional material is placed into the preoperative matrix

Figure 7. After removal of the preoperative matrix from the mouth, the final curing is accelerated with a curing light

Figure 8. The completed provisional bridge. Composite resin was bonded to the bis-acryl to compensate for the missing porcelain of the original bridge

Figure 9. Clinical photography of the adjacent teeth with shade tabs aids in communication of shade


11August 2015

Since the original bridge had fractured porcelain, com-posite resin was added to the provisional bridge to improve strength, function and esthetics (Fig. 8). A non-eugenol zinc oxide cement was syringed into the internal surfaces of the abutments’ restorations and seated. As it was anticipated that a resin cement would be used for the final case, it was important to avoid the use of eugenol in the provisional cement. A sufficient amount of temporary cement was dispensed and the margins were carefully checked with an explorer. The impression and bite registration were dis-infected and sent to the laboratory together with the lab prescription.

Shade CommunicationNumerous digital color communication technologies

have been introduced to the dental profession over the last 15 years. The most impactful device is the digital camera (Fig. 9). The use of 35 mm digital cameras to communicate color and characterization between the operatory and den-tal laboratory has dramatically reduced the most common reason for disappointment on delivery day—poor color matching.

Laboratory TechniqueProvisional Restoration

A provisional bridge can also be fabricated in the labora-tory using hybrid resin. The previously developed patient/

clinician-approved diagnostic wax-up was first matrixed with silicone putty. A duplicate cast was minimally prepared and lubricated with petroleum jelly. An initial application of enamel shade hybrid resin material was placed into the ma-trix from the heated syringe, distributed appropriately with the electric spatula, and allowed to cool. The dentin shade was then syringed into the matrix and seated on the cast while it was ensured that the matrix was completely seated. After the material was allowed to cool for four minutes, the matrix was carefully removed by first carving carefully where significant undercuts existed, to prevent damaging the uncured wax-like material. (Voids from trapped air can be repaired, if necessary, using the electric spatula.) After the hybrid resin had cooled, it was carved to develop the desired final contours and anatomy, after which the occlusal and interproximal contacts were thoroughly checked. The glaze was then applied with a disposable brush and cured. Figure 10 shows the excellent results that can be achieved using this method for a provisional for the same case.

Fabricating the Definitive FPDAll ceramic materials and technologies have exhibited

an exponential development over the previous 20 years for ceramic indirect restorative advancements. The workhorse porcelain-fused-to-metal restoration is slowly being replaced with high-strength CAD/CAM-developed ceramic materials. Development has moved through leucite-reinforced pressed

Figure 10. Provisional FPD manufactured to illustrate the excellent esthetics that can be achieved

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ceramics to pressed or machined lithium disilicate ceram-ics. The use of YZ zirconium oxide as a substrate veneered with stacked ceramics has evolved into monolithic CAD/CAM-produced restorative systems. In this case, the FPD was created with full-contour zirconia, utilizing a digitally optimized fabrication technique. Upon completion of the master cast fabrication, the casts were articulated in a cen-tric relation utilizing the provided occlusal registration.

The working cast was scanned and, utilizing the design software, the margins were identified at 100 times the actual size, thereby providing a level of accuracy that is impossible to achieve with traditional die trimming (Figs. 11-12). The virtual cement gap was determined specifically for each area of the restoration by establishing indepen-

dent parameters for margins, axial walls, the occlusal surface, and line angles. The desired external contours were transferred from a scan of the approved diagnostic wax-up (Fig. 13-16). The .stl file was then e-mailed to the central manufacturing facility for milling of the restora-tion. Upon receipt of the file, the restoration was milled from a pre-sintered zirconium oxide disk. Next, the resto-ration was dipped in the appropriate stain to achieve the desired dentine shade of the completed restoration. Finally, the restoration was sintered in an oven at 1600 degrees Celsius, fusing the zirconia particles and shrinking them by approximately 30%. The sintering process transforms the zirconia into a more dense material with high strength. The restoration was then returned to the laboratory for

Figure 12. Digital identification of margins

Figure 11. Model in 3 Shape Scanner Figure 13. Transfer of scanned diagnostic wax-up to master scan for contour determination

Figure 14. Design from buccal aspect


13August 2015

confirmation of internal, occlusal, and interproximal adaptation. After minimal adjustments were accomplished, external characterization was applied for appropriate intra-oral esthetic matching. For optimal results, A-3 Dentine was applied to the areas of wear illustrated on the buccal cusp tips of teeth #29 and 30 (Fig. 17).

Placement of the FPDThe definitive restoration was tried in to assess marginal

fit, adequate interproximal contact with the distal of tooth #28, and occlusion. A bitewing radiograph confirmed the visual inspection that marginal fit had been achieved (Fig. 18). Occlusal and interproximal contacts required no adjust-ment owing to an accurate impression, bite registration, and

meticulous laboratory work. A dual-cure resin cement was used to retain the FPD. A resin cement will adhere to the abutment tooth structure for added retention. The patient was pleased with the improved function and high esthetics of the final result (Fig. 19). The selected shade was successful in blending the opposing dentition (shade A2) with the adjacent dentition (more A3).

SummaryDentists today have a variety of materials at their disposal

for each step in the fabrication of an FPD. The successful recording of preparations, manufacture of multi-unit restora-tions, and their delivery intraorally is aided by astute atten-tion to material properties at each of these critical stages.

Figure 17. Completed full-contour zirconia fixed partial denture

Figure 18. Bitewing radiograph during try-in

Figure 15. Opposing antagonist determining final occlusion

Figure 16. Resulting design

DENTAL LEARNING

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References1. Viana PC, Correia A, Neves M, Kovacs Z, Neugbauer R. Soft Tissue Waxup and Mock-

up as Key Factors in a Treatment Plan: Case Presentation. Eur J Esthet Dent. 2012 Autumn; 7(3):310-23.

2. Garcia LT, Bohnenkamp DM. The use of diagnostic wax-ups in treatment planning. Compend Contin Educ Dent. 2003 Mar;24(3):210-2, 214.

3. Cox JR. A clinical study comparing marginal and occlusal accuracy of crowns fabricated from double-arch and complete-arch impressions. Aust Dent J. 2005 Jun;50(2):90-4.

4. Lane DA, Randall RC, Lane NS, Wilson NH. A clinical trial to compare double-arch and complete-arch impression techniques in the provision of indirect restorations. J Prosthet Dent. 2003 Feb;89(2):141-5.

5. Gordon GE, Johnson G, Drennon DG. The effect of tray selection on the accuracy of elastomeric impression materials. J Prosthet Dent 1990;63(1):12-15.

6. Phillips RW. Science of Dental Materials, ed 9. Philadelphia: Saunders, 1991.7. American National Standards Insitue and American Dental Association. ANSI/ADA

Specification #19: Dental elastomeric impression materials. Chicago, IL: American Dental Association, Council on Scientific Affairs, 2004.

8. Lee EA. Impression material selection in contemporary fixed prosthodontics: tech-nique, rationale, and indications. Compend Contin Educ Dent 2005;26(11):780-789.

9. Kaiser DA, Cavazos E Jr. Temporization techniques in fixed prosthodontics. Dent Clin North Am. 1985;29(2):403-412.

10. Grossman LI. Pulp reaction to the insertion of self-curing acrylic resin filling materi-als. J Am Dent Assoc 1953;46(3): 265-269.

11. Vahidi F. The provisional restoration. Dent Clin North Am 1987;31(3):363-381.12. Hernandez EP, Oshida Y, Platt JA, Andres CJ, Barco MT, Brown DT. Mechanical

properties of four methylmethacrylate-based resins for provisional fixed restorations. Biomed Mater Eng. 2004;14(1):107-22.

13. Christensen G. Making provisional restorations easy, predictable, and economical. J Am Dent Assoc 2004;135(5):625-627.

14. Galindo D, Soltys JL, Graser GN. Long-term reinforced fixed provisional restorations. J Prosthet Dent 1998;79(6):698-701.

15. Strassler HE, Anolik C, Frey C. High-strength, aesthetic provisional restorations using a bis-acryl composite. Dent Today 2007;261(11):128-133.

16. Lepe X, Bales D, Johnson GH. Retention of provisional crowns fabricated from two materials with the use of four temporary cements. J Prosthet Dent 1999;81(4):469-475.

17. Diaz-Arnold AM, Dunne JT, Jones AH. Microhardness of provisional fixed prosth-odontic materials. J Prosthet Dent 1999;82:525-528.

18. Reinhardt JW, Boyer DB, Stephens NH. Effects of secondary curing on indirect posterior composite resins. Oper Dent 1994;19(6):217-220.

19. Ewoldsen N, Sundar V, Bennett W, Kanya K, Magyar K. Clinical evaluation of a visible light-cured indirect composite for long-term provisionalization. J Clin Dent. 2008;19(1):37-41.

20. Pashley EL, Tao L, Pashley DH. Sealing properties of temporary filling materials. J Prosthet Dent 1988;60(3):292-297.

21. Rosentiel SF, Gegauff AG. Effect of provisional cementing agents of provisional resins. J Prosthet Dent 1988;59(1):29-33.

22. Olin PS, Rudney JD, Hill EM. Retentive strength of six temporary dental cements. Quintessence Int 1990;21(3):197-200.

23. Christensen GJ. Disinfection of tooth preparations—why and how? Clin Rep 2009;2(11):2-3.

24. Grasso CA, Caluori DM, Goldstein GR, et al. In vivo evaluation of three cleansing techniques for prepared abutment teeth. J Prosthet Dent 2002;88(4):437-441.

25. Haywood VB, Heymann HO, Scurria MS. Effects of water, speed, and experimen-tal instrumentation of finishing and polishing porcelain intra-orally. Dent Mater 1989;5(3):185-188.

26. Wiley MG. Effects of porcelain on occluding surfaces of restored teeth. J Prosthet Dent 1989;61(2):133-137.

27. Swartz ML, Phillips RW. Comparison of bacterial accumulation on rough and smooth enamel surfaces. J Periodontol 1957;28(4):304-307.

28. Tinschert J, Zwez D, Marx R, Anusavice KJ. Structural reliability of alumina-, feldspar-, leucite-, mica-, and zirconia-based ceramics. J Dent 2000;28(7):529-535.

29. Luthhardt RG, Holzhuter MS, Rudolph H, Herold V, et al. CAD/CAM-machining ef-fects on Y-TZP zirconia. Dent Mater 2004;20(7):655-662.

30. Kosmac T, Oblak C, Jevnikar P, Fundak N et al. The effect of surface grinding and sandblasting on flexural strength and reliability of Y-TZP zirconia ceramic. Dent Mater 1999;15(6):426-433.

31. Helvey GA. Finishing zirconia chairside. Inside Dent Tech 2011;2(2):62-65.32. Swartz ML, Phillips RW, Pareja C, Moore BK. In vitro degradation of cements; a

comparison of three test methods. J Prosthet Dent 1989;62(1):17-23.33. Blatz MB, Sadan A, Kern M. Resin-ceramic bonding: a review of the literature. J

Prosthet Dent 2003;89(3)268-274.34. Wegner SM, Kern M. Long-term resin bond strength to zirconia ceramic. J Adhes

Dent 2000;2(2):139-147.35. Perdigao J, Geraldeli S. Bonding characteristics of self-etching adhesives to intact

versus prepared enamel. J Esthet Restor Dent 2003;15(1):32-42.36. Weiner RS. Dental cements: a review and update. Gen Dent. 2007;55(4):357-364.37. Petrich A, VanDercreek J, Kenny K. Clinical updates: dental luting cements. Naval

Postgraduate Dental School; Bethesda, MD;26(3):1-5.38. Diaz-Arnold AM, Vargas MA, Haselton DR. Current status of luting agents for fixed

prosthodontics. J Prosth Dent 1999;81(2):139-141.

WebliographyFasbinder DJ. Clinical performance of chairside CAD/CAM restorations. JADA2006;137(9 supplement):22S–31S. Available at: http://jada.ada.org/content/137/suppl_1/22S.abstract?ijkey=24969cbaa0bb04f7453ddfdf45afb2725a09b127&keytype2=tf_ipsecshaRaigrodski AJ, Hillstead MB, Meng GK, Chung KH. Survival and complications of zirconia-based fixed dental prostheses: a systematic review. J Prosthet Dent. 2012 Mar;107(3):170-7. Abstract available at: http://www.ncbi.nlm.nih.gov/pubmed/22385693.

Figure 19. The completed full-contour zirconia bridge intraorally. Note the successful incorporation of shades A2 and A3 to match the various shades present in the same and opposing quadrants.


15August 2015

1. The value of a diagnostic wax-up in planning fixed restorative procedures is __________. a. dubious b. well-documentedc. negligible d. none of the above

2. The prepared abutment teeth are surrounded by interferences that can prevent their accurate __________. a. preparation b. bite registration c. reproductiond. all of the above

3. __________ may be used to displace the gingiva from the pre-pared margins of the abutment teeth. a. Retraction cordb. A compressive cap c. Expanding pastes d. all of the above

4. __________ can be reduced by the application of ferric sulfate. a. Gingival crevicular fluid and bloodb. Salivary flowc. Xerostomiad. all of the above

5. Double-arch trays or “triple trays” are conventionally indicated for _________. a. one to two units in opposing archesb. multiple units in opposing archesc. multiple units in the same archd. one to two units in the same arch

6. A full-arch tray is selected for bridges to give the laboratory technician more information to __________. a. correctly articulate models b. properly capture the margins c. create an accurate plane of occlusiond. a and c

7. The ability to adapt pliable material in an uncured state and to cut back borders prior to curing a custom tray minimizes __________. a. tray errors b. the curing time c. the finishing time d. none of the above

8. The two-step technique captures gross and fine detail __________. a. at the same timeb. one after the other c. poorly d. none of the above

9. __________ impression materials possess dimensional stability that permits time for transportation to a dental laboratory, and they are suitable for multiple pours without clinically significant loss of accuracy. a. Alginateb. Polyetherc. Polyvinylsiloxaned. b and c

10. An increase in room temperature __________ for impression materials. a. reduces the working timeb. increases the working timec. increases the setting time d. b and c

11. Electing to have a patient wear the provisional for an additional “trial” period before final impressions are made provides the option to _________. a. evaluate esthetics b. evaluate occlusal stability c. allow time for soft tissue healing d. all of the above

12. If a methylmethacrylate provisional is removed from the abut-ment teeth while setting and is not quickly reinserted, the shrinkage of the material may __________. a. distort the provisional’s internal aspectsb. provide for space for the luting agentc. result in an inability to seat the provisional on the abutment teeth d. a and c

13. One study showed shrinkage of bis-acryl resin to be up to __________ by volume compared to __________ for methyl methacrylate. a. 0.7%; 2%b. 1.2%; 4% c. 1.7%; 6% d. 2.2%; 8%

14. Visible-light-cured hybrid resin technology for provisional restorations offers __________. a. low solubilityb. a low wear ratec. resistance to stainingd. all of the above

15. To avoid introducing a critical crack, a light touch with __________ under copious air/water spray is advised when adjusting zirconia. a. coarse diamond bursb. fine diamond burs c. a sanding disk d. fine tungsten carbide burs

CEQuizTo complete this quiz online and immediately download your CE verifica-tion document, visit www.dentallearning.net/FPD, then log into your ac-count (or register to create an account). Upon completion and passing of the exam, you can immediately download your CE verification document. We accept Visa, MasterCard, Discover, and American Express.

DENTAL LEARNING

16


16. The use of a __________ on the preparation surfaces can reduce the hydrophilic properties of a polyvinylsiloxane impression material. a. desensitizerb. surfactant c. tubule occluding agent d. none of the above

17. Zinc oxide non-eugenol cements substitute __________ in place of eugenol. a. inorganic acidsb. organic acids c. base solutions d. none of the above

18. Using a scanner and specific design software __________. a. the margins can be identified at 100 times their actual

size b. enables accuracy that is impossible to achieve with traditional

die trimming c. helps establish independent parameters for margins, axial

walls, the occlusal surface and line anglesd. all of the above

19. Using rigid fast-set polyvinylsiloxane for the interocclusal record __________. a. results in less resistance to biting forces b. results in a faster setting timec. reduces the risk of jaw movements, while the record is setting,

that would alter the recordd. all of the above

20. Ceramics that contain glass, such as feldspar and lithium disilicate, may be predictably etched with __________. a. phosphoric acidb. hydrofluoric acid c. acetic acid d. lactic acid

21. Zirconia’s polycrystalline structure __________. a. does not contain glassb. contains apatite c. cannot form a bond to the resin cement that is as predictable

or as strong as a glass ceramicd. a and c

22. Self-etch systems __________. a. do not completely remove the smear layerb. do not penetrate into the tooth structures as deeply as other

adhesive systemsc. offer a decreased chance of post=operative sensitivityd. all of the above

23. The resin cement bond to abutment teeth is achieved using a __________ protocol. a. total-etch b. self-etchc. self-adhesive d. any of the above

24. Eugenol _________. a. is respected for its bactericidal propertiesb. can aid in reducing post-operative sensitivityc. acts as a plasticizerd. all of the above

25. _________ offer cariostatic release of fluoride from the cement to the abutment tooth. a. Glass ionomer and resin-modified glass ionomer cements b. Polycarboxylate cementsc. Zinc phosphate cements d. all of the above

26. Supragingival margins on preparations__________. a. aid hygieneb. are ideal in the esthetic zone c. compromise biologic width d. none of the above

27. Using a digital camera __________. a. aids communication about color and characterization between

the operatory and the dental laboratory b. reduces the occurrence of poor color matching c. is less effective than a written prescription for color communicationd. a and b

28. Glaze can be applied to a laboratory-fabricated hybrid resin provisional __________. a. after it has cooled b. after it has been carved to the desired final contours c. with a disposable brush and cured d. all of the above

29. Definitive luting agents are selected based upon the __________. a. condition of the abutment teethb. restorative material used for the prosthesis c. patient’s preference d. a and b

30. Due to its unique tetragonal, polycrystalline structure, _________ increases its volume around a stress-induced crack. a. leucite b. feldspathic porcelain c. zirconia d. none of the above

CE QUIZ

17OCTOBER 2012

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EDUCATIONAL OBJECTIVES1. List in detail the steps involved in fabrication of an FPD; 2. Describe the impression materials available, considerations in their selection, and the use of a

one-stage or two-stage technique;3. Review the materials and techniques available for the fabrication of provisional restorations; and4. List and review the steps involved in the fabrication of full-contour zirconia CAD/CAM restorations.

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