Biomedical subjects
Publications and source records attributed to T R Walton.
The level of predictability and high success rate of implant treatment in the anterior mandible have provided cause to re-evaluate surgical and prosthodontic protocol at our clinic. Literature relating to early/immediate functional loading of Brånemark dental implants will be discussed and preliminary results from an ongoing study will be presented.
The use of gold coating agents has been claimed to reduce residual stress in alloy-ceramic composites. The purpose of this study was to evaluate the efficacy of gold coating agents in preventing cracking of bonded porcelain. Residual stress in alloy-ceramic specimens could be increased by decreasing the coefficient of thermal expansion (alpha) of the porcelain. Vitadur-N porcelain (jacket crown type, low alpha) was mixed in increasing proportions with VMK porcelain (high alpha) to prepare five test blends with decreasing values for alpha. For each test blend, alpha was measured by means of a vitreous silica dilatometer, and varied from 13.6 x 10(-6)/K to 11.0 x 10(-6)/K. The test blends were fused around spherical specimens of a substrate alloy, Option (alpha = 14.0 x 10(-6)/K), both with and without the use of three gold coating agents, Wilkote, Spectra-Seal and Deck-Gold (normal). The composite spheres were examined under 20 x magnification after 24 hours and again after eight weeks for evidence of cracking. There was no significant difference in the failure rate of the alloy-ceramic specimens with or without any of the gold coating agents. In a bonding porcelain, alpha can be lowered in a controlled manner by the addition of varying amounts of jacket crown porcelain. Cracking of the ceramic coating occurred at and above an alpha mismatch of 1.8 x 10(-6)/K. Gold coating agents have an insignificant effect on residual stress in alloy-ceramic specimens.
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Cracking or rupturing, due to thermal stress, of porcelain bonded to a palladium-silver alloy indicated that porcelain-metal thermal compatibility was dependent on: the difference in thermal expansion coefficients of the porcelain and metal; the geometry and dimensions of the samples; and the porcelain-metal thickness ratio. A spherical configuration was more sensitive to thermal expansion coefficient differences than was a disc configuration. A higher incidence of cracking resulted from an increase in both specimen size and porcelain-metal thickness ratio.
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The flow properties of a typical zinc phosphate cement used for luting purposes were determined. These properties differed significantly from those of a Standard and a base-forming mix. An argument is presented for changing the Standard for zinc phosphate cement to recognize the different clinical uses of the material.
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PURPOSE: This article proposes a classification protocol for reporting the outcome of implant-supported fixed partial dentures. MATERIALS AND METHODS: A review of the literature revealed a contrast between the accepted criteria for assessing and presenting the outcome of osseointegrated implants and the deficient and misleading assessment and presentation of the outcome of the prostheses supported by these implants. A classification protocol comprising 6 well-defined fields with objective standards that accounts for retreatment as well as failure is proposed. This protocol has been applied where possible to reports on the outcome of fixed partial dentures in several published articles. RESULTS: In all cases there was a stark difference between the authors' claims of success and the outcome according to the 6-field protocol. It is accepted that the outcome of a given prosthesis does not necessarily correspond to the outcome of the overall prosthodontic treatment, as the latter also involves an assessment of outcome as perceived by the patient and accounts for planned revisions. CONCLUSION: If adopted, the proposed protocol would allow meaningful comparisons between prosthesis designs and between different implant systems' capacities to support such designs. It would also assist in evaluating the cost-effectiveness of implant-supported treatments.
PURPOSE: The purpose of this study was to report on the clinical characteristics and outcome of 688 single-unit metal-ceramic crowns placed in a specialist prosthodontic practice between January 1984 and December 1992. MATERIALS AND METHODS: Clinical and laboratory techniques were standardized and patients were recalled by the author between June and December of 1993. The outcome of all crowns was allocated to one of 6 fields in this assessment period. RESULTS: Clinical review examination by the author covered 87% of the crowns. Of these, 52% had been in service for 5 to 10 years and 48% for less than 5 years but more than 1 year; 67% of the crowns were placed on vital teeth and 94% were given a "good prognosis" rating at examination. The repair and failure rates of crowns in the 5 to 10 years in clinical service group were both 3%. Crowns on nonvital teeth in the same grouping had a significantly greater failure rate (5%) than crowns on vital teeth (1%), and anterior teeth had a significantly greater retreatment rate than posterior teeth. Retreatment for all 25 crowns occurred within 66 months after cementation. Tooth fracture accounted for 56% of retreatments, while caries and loss of retention accounted for only 24% of retreatments; 2% of initially vital teeth were endodontically treated during the survey period. CONCLUSION: Single-unit metal-ceramic crowns have a high expectancy of exceeding 10 years of clinical service when the described clinical and laboratory protocol is applied.
PURPOSE: This article proposes a classification protocol for reporting the outcome of implant overdentures. MATERIALS AND METHODS: Review of the literature pertaining to postinsertion prosthodontic procedures for maxillary and mandibular implant overdentures revealed a wide range in the terminology used and methods of reporting outcome, usually as a result of the use of varying designs among different implant systems. A need for comparative evaluation of the prosthodontic success of implant overdentures was identified. RESULTS: An existing classification protocol for implant-fixed prostheses containing six objectively defined fields was modified for implant overdentures. This new protocol, which also uses the descriptive fields of success, survival, unknown, dead, and retreatment (repair or failure), provides a method whereby postinsertion prosthodontic procedures and subsequent time to retreatment can be quantified regardless of design, method of attachment, or implant system. A ratio method for identifying prosthodontic treatment cost effectiveness of implant overdentures is included. CONCLUSION: This protocol could assist clinicians in their choices of implant overdenture therapy by providing accurate comparisons of varying implant overdenture systems and designs, and by identifying prosthodontic treatment cost effectiveness.
This investigation compared the accuracy of electroplated copper and stone dies. Sixty copper die replicas of a stainless steel master die were fabricated using different current settings, plating times, and backing materials. Die accuracy was assessed by measuring the misfit of a stainless steel ring machined to fit the master die. All the copper dies were more accurate than the 10 stone dies. The variability of the copper/stone dies was less than that of the stone dies (P = .011) and copper-resin dies (P < .001). There was no significant difference between the variability of the 40-mA, 48-hour copper-resin dies and the stone dies. The variability of the copper-resin dies was related to the thickness of the electrodeposit, which was a function of plating time, current, and plated surface area.
This article is the initial report of a 10-year study of all fixed prosthodontic treatment performed in a specialist prosthodontic practice between January 1983 and December 1992. A set management protocol was maintained throughout the study. Three hundred forty-four patients who underwent 411 treatment episodes involving 768 crowns and 346 fixed partial dentures (786 abutments, 599 pontics) were recalled between July and December 1993. A classification system detailing outcome with well-defined parameters and including repair requirements was developed. This report limits discussion to the study parameters and patient profile. Of the total treatment episodes, 8.5% required some form of retreatment over the survey period. Of these, 5.5% involved prostheses that had failed, and 3.0% involved prostheses that had been repaired. Females sought fixed prosthodontic treatment more than males in a ratio of 2:1. Aesthetic considerations were the most common reasons for patients seeking crowns, while replacement of failed prostheses was the predominant reason for patients seeking fixed partial dentures.