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The first three articles of this series have emphasized the importance of careful treatment planning in conventional fixed bridgework. In this, the fourth article, attention to detail continues to be the theme. The clinical procedures for fixed bridgework (tooth preparation, temporization, impression taking and occlusal registration) will be discussed.
For a variety of reasons, orthodontic intervention is often overlooked as a viable modality to correct occlusal, axial, rotational, and space discrepancies before undertaking fixed prosthetic rehabilitation. However, patient treatment is being enhanced as never before by such intervention. This valuable treatment option facilitates tooth preparation, path of insertion, optimum oral hygiene, and a better pontic and abutment design, while occlusal forces can be directed against the long axes of the teeth for a more predictable prognosis. Moreover, this interdisciplinary approach can be cost-effective to patients and their treating dentists from the standpoint of producing more stable, durable, and esthetic restorations.
Eighteen type IV dental stone dies were fabricated from a metal master die that replicated a tooth prepared to receive a metal ceramic crown. They were divided into three groups according to the type of crowns to be made: (a) machine-milled, spark-eroded titanium crowns (Procera); (b) cast titanium crowns; and (c) noble alloy crowns (as the control). The control specimens showed the smallest mean marginal openings at 25 microns and were significantly different from both the machine-milled crowns (54 microns) and the cast titanium crowns (60 microns). The two types of titanium crowns were not significantly different from each other.
The following conclusions may be made within the limitations of this investigation. - A composite resin processed directly against a roughened stainless steel dye, similar in shape to a primary anterior tooth, which has been shaped to receive a polycarbonate crown, shows the highest retentive force measured in pounds per square inch (psi). - A polmethacrylate resin, when used as a cement, also shows high values, probably due to its ability to unite chemically with polycarbonated acrylic and to its low film thickness. - Composite resins of low viscosity, low film thickness, and high compressive and tensile strengths proved also to provide good retentive values and would contribute insolubility to a greater degree than the unfilled resin. - Polycarboxylate, zinc phosphate, and reinforced zinc oxide-eugenol cements are not to be recommended as agents for cementing polycarbonate crowns. - It can be recommended on the basis of retention only, composite crowns should be fabricated directly onto the tooth preparations of carious primary anterior teeth.
While dentin-bonded crowns may hold esthetic advantages over metal-ceramic restorations, and minimal tooth preparation may also be appropriate, resistance to fracture of the restored unit is an important consideration. Dentin-bonded crowns were placed on standardized preparations in two groups of 10 maxillary premolar teeth in vitro. The preparations differed only in degree of taper. The restored specimens were subjected to compressive loading at 1 mm/min from a steel bar placed along the midline fissure. Mean fracture loads of 0.77 kN (6-degree taper) and 0.71 kN (8-degree taper) were recorded for the groups of prepared teeth, and a mean fracture load of 0.97 kN was obtained for a group of unprepared controls. Statistical analysis indicated that there was no significant difference between the fracture load of the 6-degree taper group and that of the sound control teeth.
The ability to provide patients with esthetic tooth-colored posterior restorations produced from "factory-standardized" ceramics in a single visit is a unique feature of CAD/CAM technology. Recent improvements in the hardware and computer software of the Siemens CEREC CAD/CAM System have improved its ease of use and the quality of the restoration produced. Attention to tooth preparation requirements and care in the cementing and finishing procedures remain requirements for the production of these restorations.
Porcelain veneers are the ultimate esthetic art form in dentistry. Dentists need to know the evolution of this art form and basic concepts before entering into advanced applications. Production of veneers in a laboratory or at chairside needs to be understood so that logical choices of which techniques and materials to use can be made. This article reviews history, definition, tooth preparation, variation of construction techniques, placement, clinical applications, and repair in light of recent international literature.
The effect of five dental investing techniques, three angles formed between adjoining internal pattern surfaces, and the use of a surface tension-reducing agent on air-bubble entrapment during investing were assessed. One investing technique, which mechanically mixed the investment under vacuum, invested the pattern without vacuum, then subjected the setting investment to .275 mPa of air pressure, was found to produce significantly fewer air bubbles than the other four techniques (P = 0.0096, Student's t test). The volume of the air bubbles was not found to be significantly affected by the different investing techniques, but the angle between adjoining internal pattern surfaces indicated that the more acute the angle, the larger the volume of the trapped air bubbles. When a surface tension reducer was used on the surface of patterns, pattern angles of 90 degrees had fewer trapped air bubbles than those produced with more acute tooth preparation angles, but the surface tension reducer agent had no significant effect on bubble volume. The use of a surface tension-reducing agent on the pattern surface prior to investing significantly reduced air bubble numbers (P = .054).
Previous studies on the fit of complete crowns have neglected to assess the internal adaptation of castings prior to cementation. Theoretical arguments and laboratory studies have failed to clarify which is the most desirable finish-line configuration in terms of marginal fit. This study evaluated axial and marginal fit of crowns made for three tooth preparations that had different labial finish-line configurations: shoulder, shoulder-bevel, and chamfer. The crowns were not cemented, but were sectioned and examined on their respective dies. There were no significant differences (P < or = .05) among groups for marginal or axial gaps. Crown fit was not influenced by any of the three finish lines tested, and castings with well-fitting margins exhibited measurable axial wall space.
Choosing between direct composite resins and bonded porcelain veneers to restore permanent anterior teeth requires the dentist to evaluate both the aesthetic potential and the functional reliability of available bonding procedures. Direct composites are aesthetic, conservative and reliable, but demand technical and artistic skills, and have limited longevity. Bonded porcelain veneers can have excellent aesthetics, but require additional tooth preparation, exacting technique and laboratory support, and have an unknown life expectancy.
There is some controversy about whether or not tooth preparation is needed before placing porcelain laminate veneers. Without adequate preparation, the added surface contour may increase the risk of periodontal disease. When properly executed, veneers for cosmetic dentistry should be reversible. Many teeth that could have been saved with the use of a conservative laminate veneer are destroyed by full crown reduction. The case presented in this article illustrates the preparation of six maxillary anteriors with with pronounced spaces between them for laminate veneer placement.
This in vivo study evaluated the fracture resistance of bovine teeth with prefabricated carbon fiber posts. Fourteen bovine teeth having similar lengths and dimensions were mounted in an acrylic resin block having a simulated periodontal ligament. The post space was prepared using two calibrated drills that provided an 8.5-mm post length. The prefabricated carbon fiber post was luted with a resin luting agent, and the core was made using the system's autopolymerizing resin core material. A crown was luted to each prepared tooth. Each test specimen was intermittently loaded (250 N) at an angulation of 45 degrees to the long axis of the tooth at a frequency of 2 loads per second. Four of the roots had an incomplete longitudinal fracture after loading. The results of this study were compared to a previous study by the authors that had been conducted under similar conditions with prefabricated parallel-sided posts (Para-Post) and tapered, individually cast posts. The failure rates of the two types of posts from the previous study were significantly higher (Logrank test; P<.02) than those of the carbon fiber posts.
The recent return of interest to Porcelain Jacket Crowns has been accompanied by the development of improved ceramic systems for their fabrication. One such system, In-Ceram, uses an interesting variation of the aluminous porcelain (Vitadur Alpha). It is important to realise the requirements for tooth preparation so that long lasting restorations may be produced. This article endeavours to present a method for preparation which is both efficient clinically and satisfies the physical requirements for this type of metal-free ceramic procedure.
Prosthodontists are often unaware of difficulties faced by dental technicians. Likewise, dental technicians may be unaware of difficulties faced by prosthodontists. By being better educated about one another's discipline, prosthodontists and technicians can establish cooperative goals and help each other to identify significant facts and potential difficulties posed by specific materials, techniques, or stages of the work in progress. This article describes specific procedures for prosthesis fabrication and the opportunities each step provides for such cooperation. The steps include diagnostic waxing, provisional restoration, fabrication of master dies, tooth preparation, fabrication of intraoral records, treatment waxing, selection of materials, use of ceramic mucosal simulations, and color selection. If the prosthodontist and dental technician are willing to share responsibility for treatment plans, their mutual understanding can bring new insight to old problems and provide intellectual stimulation to both.
Due to patient demand for biocompatible, safe, and tooth-colored restorations, the use of amalgam as a restorative material has been declining. Currently, the profession of operative dentistry is in a state of transition from the amalgam age to the post-amalgam age. The learning objective of this article is to discuss the current state of the art of tooth-colored restoratives--amalgam substitutes and amalgam alternatives--used either as direct or laboratory fabricated restorations nationally and internationally. Adhesive dentistry is discussed in detail, with tooth preparation as the key element. The challenges facing the clinician during the transition period include clinician education, restorative concepts and teaching competence, costs, prevention, and maintenance.
Finding an impression technique that provides a quick and accurate dental impression can be an elusive goal. The combination of a rigid, fast-setting poly(vinyl siloxane) bite registration paste and a disposable closed-mouth impression tray fulfills this goal. The comfort of the patient is enhanced because a minimal amount of the impression material, which is tasteless, is necessary. The technique enables the dentist to record habitual centric occlusion, the prepared tooth or teeth, and the opposing arch accurately and simultaneously.
This research compared the compressive strength of two types of all-ceramic crown (Hi-Ceram and Duceram) as affected by selected luting cements (Zn phosphate, glass ionomer and composite resin cement). Thirty crowns of similar size and shape were constructed (15 crowns of each tested material) to fit a standard posterior tooth preparation. Five crowns from each material were cemented by one of the tested cements. The cemented crowns were loaded until catastrophic failure. A two-way analysis of variance was performed and showed that the type of utilized cement had a significant effect on the compressive strength being that Panevia Ex. resin cement the most effective one followed by glass ionomer and then finally zn phosphate cement. Statistical analysis also showed that Hi-Ceram crowns were more resistant to occlusal load than Duceram.
A new technique for tooth-colored inlay cementation is introduced. Dual-cure fully filled restorative resin Sono-Cem (ESPE America, Norristown, PA) was used to cement tooth-colored restoration. A specially designed wooden tip in the gently vibrating Profin handpiece (Dentatus USA, New York) may be considered an excellent instrument for cementing porcelain and composite inlays with Sono-Cem cement. Also, a wide variety of diamond/tungsten plated abrasive Lamineer tips in a Profin Handpiece may be used for tooth preparation as well as for finishing restorations.