In vitro retention force changes of prefabricated attachments for overdentures.

Changes in the retention force of six prefabricated spherical and cylindrical attachments were examined in vitro under continuous loading. The testing machine permitted insertion-separation cycles to be tested under reproducible conditions while a calibrated measuring device determined the insertion and retention forces. At the beginning, during the so-called run-in period, all anchoring elements showed a very unstable behaviour characterized by a varying marked increase and subsequent decrease in the retention force. During the ensuing functional period, the retention force followed a more stable course. In this phase, the frictional attachments having lamellae for activation proved more stable than did the spring-loaded retention attachments. Furthermore, in two of five cylindrical anchors by Gerber, the spring broke. This provides support to the concept that prefabricated attachments should be constructed as robust elements composed of as few individual parts as possible. This would help to ensure that service and repairs remain at a minimum. Frictional attachments with lamellae for activation are to be preferred for use in matrices and patrices over attachments having spring-loaded retention.

Treatment with removable partial dentures: a longitudinal study. Part II.

The aim of this study was to evaluate the effectiveness of an oral rehabilitation by removable partial denture (RPD). Between 1983 and 1994, 629 patients were provided with an RPD at the Dental School of the Université catholique de Louvain. All the RPDs were constructed with a cobalt-chromium framework. All the treatments were provided by dental students under the supervision of clinical instructors. At recall time (1998-2000), 269 patients could not be reached neither by telephone nor by mail and 27 had died. Consequently, 333 patients were called for clinical examination and 254 of these (76.3%) actually attended. For a total of 292 RPDs checked 1893 persistent teeth were listed, with 804 serving as abutments; more than half (57.6%) of these were crowned, for which 51 debondings were recorded. For the period of observation we listed 79 abutments lost (37 at the upper jaw and 42 at the lower jaw), i.e. 9.8% of the total number of abutments. No relation could be established between the type of the abutments (natural or crowned teeth) and the losses observed (Test of Mantel-Haenszel: P=0.9496). In the upper jaw, the percentage of abutments lost was significantly higher in the presence of free-end edentulous areas as compared with bounded edentulous areas (Test of Mantel-Haenszel: P=0.0002); this difference does not appear for the lower jaws (P=0.9558). If we deduct the 25 abutments related with the 11 non-worn RPDs and the 79 abutments lost, no change becomes apparent for 92.2% of the maxillary abutments and for 85.8% of the mandibular abutments. For the 1089 other teeth, we observed the loss of 40 teeth and the appearance of caries or new fillings for 95 teeth. The fractures of cast clasps represent 3.4%.

Stress distribution of abutments and base displacement with precision attachment- and telescopic crown-retained removable partial dentures.

Five types of removable partial dentures (two attachment dentures, two telescopic dentures and one clasp denture) were designed. The two attachment dentures were retained by the rigid-precision attachments with or without a stabilizing arm, and the two telescope dentures were retained with cone telescope crowns with or without cross-arch stabilization. The stresses acting on abutment teeth and denture bases and the movements of denture bases were investigated, and the influences of denture design were clarified. The stress acting on a terminal abutment tooth retained by a rigid-precision attachment or cone telescopic crown was larger than that acting on a terminal abutment tooth retained by a clasp. The attachment dentures tended to concentrate more stress at the terminal abutment tooth than did the telescopic dentures. The stress of denture base of an attachment denture and a telescopic denture was less than that of a clasp denture. There was no difference between the stresses of attachment and telescopic dentures. The displacement of the denture base tended to be less when the denture was designed with a rigid connection for the retainer and with cross-arch stabilization.

Elementos retentivos en sobredentaduras: reporte de un caso clínico / Retentive elements in overdentures. Report of a clinical case

Los tratamientos de sobredentaduras están tomando cada vez más auge debido a que la población tiene una mayor educación respecto a su salud oral, además de que los odontólogos están mejor capacitados para realizar este tipo de tratamiento. En este artículo se pretende ilustrar las diferentes opciones de aditamentos que se tienen para aumentar la retención y estabilidad de la dentadura y se presentan las características de los aditamentos Preci-ball son fáciles de conseguir, sus procedimientos clínicos y de laboratorio son sencillos y rápidos, son maquinados en aleación oro o paladio y limpiados fácilmente

Consideraciones estéticas en el diseño de retenedores directos de prótesis parciales removibles / Esthetic considerations in the design of direct retainers for removable partial dentures

La P.R.P. retenida con ganchos constituye un problema estético que puede ser minimizado a través de un adecuado análisis y diseño del caso. La utilización del aditamento ofrece la ventaja de obtener excelentes restultados estéticos al eliminar el brazo retentivo vestibular de los ganchos; sin embargo, la utilización de éstos representa trabajo adicional para el odontólogo y mayor costo para el paciente; además, el uso de estos aditamentos es un tema controversial y confuso en la especialidad debido a la multitud de alternativas, como son aditamentos intracoronales, extracoronales, intrarradiculares, extrarradiculares, de precisión, de smiprecisión, rígido y elásticos. En esta revisión se presentan algunas consideraciones estéticas en el diseño de retenedores directos, así como la nomenclatura, clasificación e indicaciones de los diferentes tipos de aditamentos utilizados como retenedores de P.P.R. y los criterios para su selección

Sobredentaduras: Evaluación de los sistemas de retención, parte II / Overdentures: evaluation of the retention systems, part 2

Sin éxito a lo largo del tiempo, la prostodoncia trató de superar los inconveninentes presentados por los pacientes portadores de prótesis completa; frente a las exigencias de los edéntulos y en la búsqueda de mejorar esta situación incómoda y tediosa para el paciente y el profesional, aparecen las prótesis removibles y sobredentaduras sobre raíces e implantes solos o combinándose entre sí. Señalando sus ventajas y desventajas; razones diagnósticas para su aplicación, obteniendo una clasificación de acuerdo a su función. Se hace incapié en la planificación preprotética, clave para el éxito de nuestra prótesis; no improvisando, y compartiendo con el laboratorista, desde la concepción hasta la instalación, desde el análisis del terreno donde se trabaja, la búsqueda de retención y estabilidad, con la inclusión de la biomecánica de los materiales; harán en su conjunto el objetivo de nuestro trabajo. Realizando una selección de las conexiones retentivas existentes; describiendo los magnetos, broches, barras, analizando sus indicaciones y contraindicaciones; dadas las exigencias de todos los pasos clínicos, se estará en la observación del efecto sobre el periodonto, la neuro-musculatura, evitando la parafunción y de los elementos retentivos entre sí; recalcando la colaboración de nuestros pacientes con su higiene oral, para ver satisfechos los esfuerzos puestos en la clínica y en el laboratorio

A simplified system to develop precision master models.

Master model construction using a plexiglass base is a procedure used in many dental laboratories. The following technique uses the Compact System to create a precision master model. This system is functionally superior to pour and base techniques because of its improved precision, better placement and improved cleanliness of the holes that receive the dowel pins.

Relaçäo entre o arco dental estabelecido e a crista do rebordo alveolar em prótese total / Relationship between the established dental arch and crest of the alveolar ridge in complete prostheses

Realizou-se um estudo das relaçöes entre as cristas dos rebordos alveolares, superiores e inferiores, e as posiçöes dos arcos dentais estabelecidos proteticamente, antes e após a montagem dos dentes. Verificou-se que a relaçäo em questäo se distribui segundo três padröes básicos: a) crista do rebordo envolvendo o arco dental, que foi chamado padräo "envolvente"; b) crista do rebordo coincidindo com o contorno do arco, que foi denominado "coincidente", e c) crista envolvida pelo arco dental, que foi chamado de "envolvido". Desses padröes, a maior freqüencia foi do padräo "envolvido", sendo 76,66 por cento nas próteses superiores e 60,0 por cento nas inferiores

Sobredentaduras retenidas por ataches esféricos de implantes oseointegrados mediante la aplicación de un compuesto polixilano vinílico / Osseointegrated implant overdenture retained by ball attachments through the application of a vinyl-siloxane compound

Se describe un estudio clínico radiológico lineal en 15 pacientes donde se usaron esferas retentivas ("bola atache") para soportar prótesis completas inferiores y un compuesto polisiloxano vinílico para su fijación y retención. El plazo de seguimiento fue hasta de 5 años, correspondiendo: sexo: 6 masculinos, 9 femeninos; edad: 40 a 70 años. Los resultados muestran características satisfactorias ya que la reabsorción ósea controlada radiográficamente y corroborada por sonda roma de plástico, se presenta próxima a 1 mm. Fuerzas traumáticas pueden determinar algún fenómeno más pronunciado obedeciendo a circunstancias esencialmente locales y en relación a un sector del implante. La edad permite resultados muy satisfactorios en personas jóvenes, y el sexo no marcó diferencias significativas. Se describen las modificaciones de la técnica clásica en la aplicación de retenedores esféricos en forma directa y la utilización de un elastómero de consistencia fluida (polisiloxano vinílico de impresión de corrección) para lograr la fijación y retención de esta prótesis a los retenedores ("bola atache"), calculada por dinamómetro en 400 a 450 grs. Su aplicación en forma directa permite una adecuada oclusión que compensa el esfuerzo masticatorio y la resiliencia de la mucosa. El estudio clínico radiológico y el diagnóstico implantoprotético son condiciones fundamentales para determinar el número, diámetro y ubicación de los implantes con sus respectivas esferas retentivas

[A device for fixation of partial removable dentures in cases of single-standing teeth]. / Ustroistvo dlia fiksatsii chastichnykh s''emnykh protezov pri odinochno stoiashchikh zubakh.

An outfit for fixing removable dentures in single standing teeth contains internal and external telescopic crowns. The latter is fitted out with a clasp and a cut-out on the oral surface. In order to enhance the design rigidity and denture fixation safety, the two-layer internal crown is placed on the vestibular and approximate surfaces, whereas the clasp on the external layer thereof.

Stress distribution within circumferential clasp arms.

An analysis of stress distributions within circumferential clasp arms with various tapers, was undertaken in an effort to (1) determine the area of maximum stress concentration in both tapered and non-tapered clasps, and (2) to compare this point of maximum stress concentration with the area of frequent clasp breakage. The non-tapered clasp showed better distribution of stresses than the tapered clasps. The less favourable stress concentrations could result in eventual failure of the clasp when coupled with other factors such as porosities. The maximum shear stresses in the non-tapered clasp also were lower than those in the tapered clasps. As the taper of the clasp became more accentuated, the magnitude of the stresses increased and shifted towards the tip of the clasp. The maximum tensile stress calculated in a replica of a chromium-cobalt-nickel clasp was in the order of 34 MN/m2 which is well below the ultimate tensile strength of the alloy. This observation leads to the proposal that failure of clasps is a function not only of design but also of other variables, such as porosities, surface irregularities, and fatigue.