Abutment Crown Research Articles

Measuring Accuracy of the Shoulder of the Crown Abutment by Using the Experimentally Developed Laser Digitizer

Measuring Accuracy of the Shoulder of the Crown Abutment by Using the Experimentally Developed Laser Digitizer

Fabricating abutment crowns for existing removable partial dentures using custom resin clasp analogs

A universal approach for fabricating abutment crowns for existing removable partial dentures is described. A replica (analog) of the clasp assembly is generated and transferred to a traditional working cast, which includes the abutment die. The analog is incorporated into the working cast as a removable component to allow the formation of the crown contours. The article reviews in detail the procedures required to transfer accurately all the essential components and information from the mouth to the working cast while allowing the patient uninterrupted use of the removable partial denture. Prestabilizing the removable partial denture, creating the analog impression, avoiding errors due to soft tissue components, forming a precise analog base, selecting materials, generating a rigid resin analog, and prescribing a path of insertion and withdrawal to the analog are described. The method replicates all types of clasps and can generate all types of fixed prosthodontic retainers to function harmoniously with the existing partial denture. (J Prosthet Dent 1998;80:619-29.)

Treatment injuries in dentistry – cases from one year in the Swedish Patient Insurance Scheme

Eight hundred and fifty-one claims submitted to the Swedish Patient Insurance Scheme were studied and analysed. The most frequent claim referred to root fractures of roots with posts, and to root perforations also related to root posts. Other relatively frequent claims referred to pulpal complications in connection with fixed prosthodontics, root perforations related to endodontic treatment, and dysaesthesia. The mean latency time (the time from the actual treatment to the diagnosis of the injury) was for root fractures 10.6 months, and the mean latency time for root perforations that were not directly observed during preparation was 15.9 months. Pulpal complications of teeth treated with crowns or fixed partial dentures had a mean latency time of 7.6 months. Injuries with a low frequency were, for example, fracture of vital abutments for crowns or fixed partial dentures, damage to tissue by electrosurgery or to the floor of the mouth by drilling, or perforations to the antrum. Two cases of particles dropped into the patient's eye were also reported.

Unanticipated outcomes: dental implants.

Dental surgical implant treatment modalities continue to be relatively successful within musculoskeletal restorative systems. Because available systems include a wide range of metallic and ceramic biomaterials plus multiple designs for the implant body, transgingival abutment, and intraoral crown constructs, failure analyses of explanted devices must include comprehensive information. The current opinions are based on approximately 4000 musculoskeletal implant device studies conducted from 1970 to 1997. As a subset, the dental systems with and without calcium phosphate ceramic on the endosteal portion of the implants will be considered at 0 to 1, 1 to 5, 5 to 10, and beyond 10 years in vivo. Observations will be reported and opinions provided about the advantages and disadvantages of ceramic coated implant systems.

A provisional and new crown to fit into a clasp of an existing removable partial denture

A technique that forms an abutment crown to fit into an existing clasp of a removable partial denture by relining an acrylic resin pattern is described. The outer contour of the pattern is made within an irreversible hydrocolloid impression by use of Duralay autopolymerizing acrylic resin applied with precision dispensers. The pattern is formed before tooth preparation and is made approximately 0.4 mm thick. After tooth preparation, the shell pattern is relined with the same autopolymerizing resin and the existing removable partial denture is fitted over it. The gross pattern is trimmed and the margins refined on a die made from an elastomer impression. The refined pattern is cast and finished, avoiding reduction of the contours established. A second crown is similarly formed in tooth-colored autopolymerizing acrylic resin. It serves as a provisional restoration that allows the patient to wear the removable partial denture while the laboratory procedures are performed.

The seating of one-piece and soldered fixed partial dentures

This laboratory study compared the seating of one-piece castings with that of soldered fixed partial dentures. Two investments were investigated, five American Dental Association type III and five metal ceramic alloy fixed partial dentures were made by using the conventional indirect technique. The investing and casting protocol was designed to produce an ideal fit of the individual complete crown abutments, not the fixed partial denture. Independent seating of each retainer provided a baseline measurement for complete seating and was compared with fixed partial denture seating. Fixed partial dentures were then sectioned and reassembled by soldering twice, using a low- and high-expansion investment. Statistical evaluation identified significant differences between the metals and the techniques. Marginal discrepancies with one-piece casting and lower (0.6%) thermal-expansion soldering were clinically unacceptable. A clinically acceptable fit was obtained with the higher (1%) thermal-expansion soldering investment.

Metal-porcelain bonding to a magnetizable alloy

The bond strength of porcelain to a magnetizable Pd-Co alloy was compared with that of a precious and nonprecious ceramic alloy by using the four-point flexure test and a direct shear test. The test procedure consisted of continuous loading until a bond failure occurred. The fractured surfaces were then examined with a scanning electron microscope. A good strength of the magnetizable Pd-Co alloy comparable to that of two specific ceramic alloys and intermediate between precious and nonprecious alloys was observed. Most of the failures of the precious alloy occurred at the oxide-porcelain interface. The preferential fracture paths were observed for the nonprecious alloy between the metal fracture and the oxide layer. The fractures of the magnetizable alloy occurred at the oxide-porcelain interface and in the bulk of the porcelain, clearly pointing out the possibility of using magnetizable Pd-Co alloy for metal ceramic abutment crowns.

全部鋳造冠の印象採得における個歯トレーの有効性についての臨床的検討

This study was executed at an opportunity for taking the impressions of a full crown abutment tooth by the five different methods with the four different impression materials; the copper ring tray on the abutment method with the polysulfide rubber, the resin ring tray on the abutment method with silicone rubber, the wash technique with silicone rubber, the hydrocolloid impression technique and the hydrocolloid-alginate impression technique. The reproducibility of the preparation margin on the ten stone dies was photographically measured and the following results were obtained. 1. The reproducibility of the preparation margin was affected considerably by the following conditions. 1) The character of the impression materials, 2) the position of the preparation margin in the gingiva sulcus and 3 the undercut degree beneath the preparation margin. 2. The impression technique with the individual ring tray on the abutment showed great utility under any condition of the preparation margin on the abutment. 3. The impression method should be selected clinically according to the condition of the abutment.

Distribution of occlusal forces along unilateral posterior two-unit cantilever segments in cross-arch fixed partial dentures

Axially directed occlusal forces over unilateral posterior two-unit cantilever segments of cross-arch fixed partial dentures were measured during natural functioning by using built-in transducers, one in each cantilever unit. The mean local maximal occluding and maximal chewing forces were significantly larger over the first (124 N and 64 N) than over the second (21 N and 29 N) cantilever unit. The average intraindividual ratio between the forces over the first and second cantilever unit amounted to 12:1 for maximal occlusion and 3:1 for maximal chewing. Despite the smaller mean total maximal chewing (92 N) than mean total maximal occluding cantilever force (145 N), the resulting axially directed mean bending moments in the joint between the distal abutment crown and the cantilever segment did not differ significantly. This is explained by the larger mean maximal chewing (29 N) than mean maximal occluding (21 N) force over the second cantilever unit. This demonstrated that not only the magnitude of occluding and chewing forces over cantilever segments but also their distribution along the cantilevers is of importance for the magnitude of functional stress created in cantilever fixed prosthesis.

Accuracy of impression materials for complete-arch fixed partial dentures

The accuracy of 12 impression materials of six different types were studied by using complete-arch FPD impressions. Sixty impressions were made of a Columbia dentoform maxillary model with complete cast crown abutment preparations on the canines and the second molars. A one-piece casting was constructed by connecting the four individual castings made for the four abutment teeth. The master prosthesis was seated on the stone casts produced from the impressions. The marginal adaptation on the four abutments was then evaluated with a travelling microscope. The individual marginal adaptation of the four castings on the abutments was also examined after sectioning the four joints. The following conclusions were drawn. 1. The polyethers produced the most accurate complete-arch replicas. The second most accurate were the vinyl polysiloxanes, followed by the polysulfides and the irreversible-reversible hydrocolloids. The least accurate were the reversible hydrocolloids and the irreversible hydrocolloids. 2. The polyether impression materials exhibited the most consistent accuracy for a master cast to fabricate a complete-arch FPD.

Use of a paralleling post for cast orientation when fabricating removable partial denture abutment crowns

Use of a paralleling post for cast orientation when fabricating removable partial denture abutment crowns

An articulator and surveyor remount technique for surveyed abutment crowns

An articulator and surveyor remount technique for surveyed abutment crowns

Magnetizable abutment crowns for distal-extension removable partial dentures

A study of the retention and load-distributing characteristics of bilateral distal-extension dentures with magnetizable abutment crowns revealed the following findings: Comparable retention was obtained with the horizontal and oblique pedestals. Decreased retention was noted when there was space between the magnet and pedestal. The retention values were substantially higher than reported values for the I-bar retainer. For the space and no-space situations, the horizontal pedestal design provided better stress results than the oblique design. Better stress-distributing properties for horizontal and oblique pedestals were obtained with the presence of a space between the magnets and pedestals. Of all the designs tested, the horizontal pedestal with a space demonstrated the best load-transmission characteristics.

Spatial changes occurring in fixed partial dentures made as one-piece castings

U se of base metal alloys to make the metal framework of ceramic veneered crowns and fixed partial dentures has created the need for technical modification in procedures previously applied to gold base ceramic alloys. Making one-piece metal castings for multipleunit fixed partial dentures is one of the more notable technical modifications, since in preand postsoldering procedures it has been difficult to achieve a strong, dependable solder joint in the base metal framework. Thus, one specific problem is assessing the degree of dimensional accuracy in casting a one-piece base metal fixed partial denture. Studies on casting accuracy for single crowns1-4 and multiple-unit fixed partial dentures5-* reported marginal discrepancies after cast specimens were returned to dies of origin. In general, these investigations determined casting accuracy by observing the closeness by which the margin(s) of castings and margin(s) of dies could be brought into apposition. Suffert and Mahler’ suggested that inherent surface roughness of the casting influenced fit and that this variable could create confusion in making an assessment of casting fit. This study was designed to establish a method of assessing the dimensional changes occurring at the margins of a multiple-unit fixed partial denture. The distances between specific precast (wax stage) and postcast (metal stage) points on abutment crown margins were recorded in conjunction with alterations in the expansion of investment material. Comparisons of these measurements provided an evaluation of the accuracies of the castings.

Replacing an abutment crown for an existing removable partial denture

A method to replace an abutment crown for an existing removable partial denture has been presented.

試作並びに市販支台築造用コンポジットレジンの機械的性質に関する基礎的研究

試作並びに市販支台築造用コンポジットレジンの機械的性質に関する基礎的研究

Dinarnic Study on the Force Distribution of Various Forms of Full-cast Crown Abutment Teeth

There are many studies on the full cast crown, but the all-out dynamic studies foraxial, ocolusal and margunal form, that is very important factors, have not been find. The author tries to analyze the dynamic effect of differences of full cast crown abutment on the abutment, then the two-dimesnional photoelastic studies are carried out. The maxillar bicuspid for specimens is bucco-lingual synmetrical form, and the specimens being enlarged the three times of this teeth. are made by the B-hardner #901. The photoelastic apparatus, product of the Riken-keiki Co., is used for this study. The load direction is arranged at the long axis of specimen, the monochromatic fringe photographes are taken and analyzed.The abutment forms of full cast crown consist of three factors, that is the axial angle (5, 10, 20 and 30 degrees), the cusp angle (0, 10, 20, 30 and 40 degrees) and the marginal form (knife edge type, chamfer edge type, bevel edge type, bevel-shoulder edge type and shoulder edge type), and are carried out to analyze by the two-dimensional photoelastic test. Futhermore, the specimens with the axial angle of 5 degrees the cusp angle of 30 degrees are preparated of three marginal forms (knife edge type, chamfer edge type and shoulder edge type) and they are analyzed. The dynamic effects of differences of abutment forms on the abutment are investigated and the following conclusions are obtained.1. Regarding the axial angles, the each specimen with 5, 10, 20 and 30 degrees is researched. The maximum stress concentration in each specimen is observed at the pulp horn. Its value is tend to increase according as the axial angle increases. Therefore, it is concluded that theless the axial angle is, the more the abutment is dynamically. Consquently, the best axial angle is 5 degrees.2. As regards the cusp angle, the each specimen with 0, 10, 20, 30 and 40 degrees is studies. The strees concentration is observed at the pulp horn and margin. It is find that the more the cusp angle increases, the less its values are. Then, the cusp angle is best according as it increase, especially, it is effect as to decrease the stress concentration at the pulp horn and margin.3. As for the marginal forms, the specimens with knife edge type, chamfer edge type, bevel edge type, bevel-shoulder edge type and shoulder edge type are investigated. Regarding the stress concentration at the pulp horn, the knife edge type is minimum, and the chamfer edge type, bevel edge type, bevelshoulder edge type and shoulder edge type are increased in order of magnitude. Consquently, the knife edge type is best, the chamfer edge type, bevel edge type, bevel-shoulder edge type and shoulder edge type are in order of magnitude.4. As regards the specimen with the axial angle of 5 degrees and the cusp angle of 30 degrees being preparated for the marginal forms of knife edge type, chamfer edge type and shoulder edge type, the knife edge type is best. The chamfer edge type and shoulder edge type is in order of stability. In case of the shoulder edge type with the cusp angle of 30 degrees, the stress of margin and pulp horn is remarkably decreased. As to use of this type, this is careful consideration.

Dynamic Studies on the Force Distribution of Various Forms of Full Cast Crown Abutment Teeth

There are a lot of studies on the abutment teeth of the full cast crown, and its reasonable forms were investigated with the photoelastic studies from a dynamic point of view. The two-dimensional studies have mainly been found, but the three-dimensional photoelastic ones have been researched little.So as to analyze the stress concentration at the inner part of abutment on the axis, occlusal face and marginal form, the author carried out the three-dimensional photoelastic studies applied to the anatomical solid specimen.To insure uniformity of the specimens tested, the basic plaster model is the simplified form of the maxillary second premolar enlarged three times. The epoxy specimens were made of the master model.The abutment models consist of three groups and nine kinds, that is A group (cusp angle: 0°, marginal form knife-edge, axial angle: 5°, 10° and 20°), the B group (axial angle: 10°, marginal form: knife-edge, cusp angle: 10°, 20° and 30°) and the C group (axial angle: 10°, cusp angle: 0°, marginal form: bevel-edge, chamfer-edge and shoulder-edge).The photoelastic and stress freezing apparatus, product of Riken-Keiki Co., are used for these studies. The load direction was applied to the long axis of the specimens, and the resulting isochromatic fringe patterns of each section in the specimens were recorded photoelastically. The circumferential stress distribution of each specimen was analyzed and the following conclusions were obtained.1. In all of the specimens, the highest concentration of stress was observed at the cervical area, but the stress was not concentrated in the area of the pulp horns.2. The stress in the cervical marginal area with the buccolingual section of axialangle 20° and the mesio-distal section of axial angle 10° showed the least concentration.3. The stress concentration in the cervical marginal area is decreased, when the cusp angle is increased. And it exhibits very little stress at the cusp angle of 30°.4. The marginal form of the chamfer-edge developed a tendency to have the same degree stress as did the bevel-edge is best mechanically. The end of the marginal ledge with the shoulder-edge showed very higher stress concentration. The knife-edge showed much higher stress concentration at the end of the marginel ledge.

Copper-band impressions for complete crown abutments

I he adaptation of a complete crown to the gingival margin is an important factor for the sound prognosis of teeth. Ill-fitting margins contribute to the accumulation of bacterial plaque and thus predispose the tooth to caries and periodontal disease.’ Therefore, an exact reproduction of the abutment at the finishing line of the preparation is of particular importance among the several factors’ governing the proper seating of complete crowns. Since the impressions must also include a narrow zone of unprepared tooth hurface immediately apical to the finishing line, they are usually removed over more or less pronounced undercuts. Consequently, the impressions are highly liable to deformation in this critical area. This clinical problem has been greatly reduced in recent years by the introduction of the tray impression technique combined with highly elastic impression materials. However, individual impressions of each abutmc’tlt using relatively tight-fitting impression bands are still preferred in SOIII~ c,lirricnl instances. Both thermoplastic and elastic compounds are commonly used with this technique. A description of their physical properties will give a clue to the range of indication for each material, but little seems to have been done to stud) thfair suitability specifically for the copper-band technique. The present investigation studied the applicability of one thermoplastic material and different types of elastic materials for the copper-band technique. The impressiol t technique simulated the clinical method, often resorting to relatively tightfitting bands when the application ‘of impression material subgingivally is difficult. Impressions were taken of abutments with varying degrees of taper belobv the finish ing line. The impressions were inspected for rupture of the materials, and the exactIIC~ of intact impressions \vas measured indirectly on stone dies. Finally, a siniplt% rntxthod to avoid deformation of elastic impressions in soft copper bands evolved.

Fixed splint for widely spaced mobile teeth

A fixed periodontal splint can be made for teeth with wide interproximal spaces by joining the abutment crowns with palatal bars. Missing teeth can be replaced by attaching pontics to the main lingual bar. The bar splint provides adequate tooth stabilization, without the necessity for making unesthetic oversized crowns.