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Purpose: This article presents a rationale for retrievability of fixed, implant-supported prostheses based on the incidence and variety of biologic and technical complications. The etiologies of these complications are also discussed, emphasizing the unpredictability of implant-based prostheses in the oral environment. Materials and Methods: Electronic searches of the MEDLINE (Ovid) database were initially conducted to find articles in English relating to the incidences and/or etiologies of dental implant complications up to May 2006. These articles were then manually searched and potential papers investigated. Electronic and manual searches of 11 peer-reviewed dental journals completed the research strategy, with a hierarchy of evidence-based information established to support this complication-based analysis. Results: Biologic and technical complications appear to be common in all forms of fixed implant-supported dentistry. These complications often jeopardize the functional and/or esthetic features of a given prosthesis, and they occur despite sound prosthetic design and high levels of clinical expertise. Observational studies and systematic reviews dominate this area of the dental literature, leaving the clinician to individually assess the merits of prosthetic retrievability based only on the likelihood of complications and the costs of replacing a permanently cemented prosthesis. These assessments challenge the philosophy of permanent cementation, but there is a need for better, evidence-based information to properly evaluate the costs of prosthetic retrievability against the obvious clinical benefits. Conclusion: The practice of permanently cementing implant-based prostheses may conflict with the likelihood of biologic and technical failure. The retrievability of fixed, implant-supported prostheses is therefore an important consideration in delivering quality, patient-based treatment outcomes. [ABSTRACT FROM AUTHOR]

Purpose: This study investigated the effects of low seating force (5 N) with and without oscillation on pulpward pressure transmission during crown cementation. Materials and Methods: Thirty human premolars received standardized complete-crown preparations. They were randomly allocated into three experimental groups of ten: group 1 = 100-N static load; group 2 = 5-N static load; and group 3 = 5-N load with oscillation. Crowns were constructed of base-metal alloy and attached to a purpose-built loading device. Pulpal pressures were recorded using a 0- to 104-kPa pressure transducer that was connected via the sectioned root of the premolar to the pulp chamber, which was perfused with saline driven by nitrogen gas at 83 kPa until a steady rate was achieved. The crowns were cemented using zinc phosphate cement, and postcementation elevations were measured with a linear variable differential transformer. An amalgam condenser provided oscillation for 1 minute. Results: The pulpal pressures were: group 1 = 455 Pa; group 2 = 26 Pa; and group 3 = 76 Pa. The postcementation crown elevations were: group 1 = -48 µm; group 2 = 362 µm; and group 3 = 26 µm. Conclusion: Acceptable crown seating can be obtained using low force (5 N) combined with oscillation, and lower pressure pulses are generated compared to using high force (100 N) alone. [ABSTRACT FROM AUTHOR]

Purpose: The determination of an acceptable occlusal plane is essential for the development of esthetic prosthodontic restorations. However, since most faces are not symmetric, a method was developed for measuring facial angular asymmetry, ie, the divergence from the vertical or horizontal of the line joining the midpoint of the intercanthal line and the philtrum of the lip, the interpupillary line, the intermeatal line, the lip commissure line, and the intercuspid line. Materials and Methods: Standardized frontal images (mouth closed, smiling, and biting on a wooden spatula) of 100 subjects were taken using a digital camera. These images were downloaded into a computer, and the angles between the various facial lines and the horizontal were measured. The subjects were grouped by sex, age, and history of trauma and orthodontic treatment. Results: No statistically significant differences were found between the mean values for each group. Conclusion: Asymmetry of the face can be measured using digital camera imaging and computer analysis. A range of facial asymmetries that can influence the choice of occlusal plane during prosthodontic treatment exists. Thus, the use of an occlusal plane parallel to the ala tragus and interpupillary lines, as often advocated by prosthodontists, may result in less than ideal esthetics in the final restoration. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to determine pressure changes in the pulp space during tooth preparation with either diamond or tungsten carbide burs in a high-speed dental handpiece in the laboratory. Materials and Methods: Twenty premolar teeth were collected and randomly assigned to two groups: group 1 received preparation with diamond buys and group 2 with tungsten carbide burs. The teeth were mounted on a pressure transducer and the pulp chambers were filled with saline. A 0.1-mm thickness of tooth tissue was removed from the proximal surface of each tooth, alternating dry and wet cutting, until the pulp chamber was exposed. Pressure and temperature changes were recorded during tooth preparation. Results: At 0 to 1 mm of remaining dentin depth dry cutting with diamond and tungsten carbide burs generated a mean positive pulpal pressure of 12 kPa and 6 kPa, respectively. Wet cutting under the same conditions produced 0.6 kPa and 0.15 kPa, respectively. The difference between wet and dry cutting was highly significant (P < 0.001). Diamond burs produced significantly higher pressure increases than carbide burs at all levels for both wet and dry techniques (P < 0.05). When cutting farther than 2 mm from the pulp, tooth preparation created a mean 0,09-kPa pressure increase, which was not influenced by either coolant use or bur type. The temperature change was minimal during wet cutting and only minor temperature increases were recorded during dry cutting. Conclusion: From this laboratory study it is concluded that significant pressure changes occur in the pulp chamber during tooth preparation of extracted teeth when the remaining dentin thickness is less than 2 mm. [ABSTRACT FROM AUTHOR]

Ten extracted molar teeth were prepared to a standardised complete crown preparation. Five stone dies were constructed for each tooth and coated with zero, two, four, six, and eight layers of a paint-on die-spacer. Crowns were fabricated on each die and the force required for removal from each tooth was measured prior to cementation. The crown elevation and force required for removal were measured after luting with zinc phosphate cement. The force required to remove the crowns before cementation decreased with increasing layers of die-spacer. Following cementation, the mean crown elevation decreased from 547 μm (zero layers) to 38 μm (eight layers); while the mean removal force increased from 250 N (zero layers) to 375 N (eight layers). [ABSTRACT FROM AUTHOR]

Stainless steel dies, simulating 0 to 80 μm of die spacing, were seated into a machined brass crown with Phosphacap, Panavia EX, and C & B Metabond. The seating discrepancy after 60 seconds was measured to determine the optimal cement space for best seating for each agent. The most complete seating for crowns luted with zinc phosphate cement was observed when at least 40 μm of cement space was provided. C & B Metabond and Panavia required 30 μm of die spacing. [ABSTRACT FROM AUTHOR]