Effect of thickness of peridental restorations on the casting precision

The present study has shown that the precision of peridental gold alloy castings depends both on the specific properties of the investment used and on the thickness of the pattern. In all cases the inside diameter of the castings decreased with increasing thickness. The most accurate results were obtained with an experimental investment characterized by a setting expansion of 0.05%, a thermal expansion high enough to compensate for the alloy contraction during cooling from solidus to room temperature, and a compressive strength of only 27 kg/cm² at 67O° C.     

A modified phosphate-bonded casting investment

Abstract – An experimental phosphate-bonded casting investment with negligible setting'expansion and a thermal expansion of 1.6%, sufficient to compensate for the solid thermal shrinkage of conventional dental gold alloys and high-precious alloys for die porcelain fused to metal technique, is described. When used in a ringless casting technique the investment makes it possible to produce cast restorations with a consistent slidefit. In combination with a die spacer technique the new investment makes it possible routinely to produce cast restorations with a consistent and known, degree of loosefu.     

An improved dental casting investment

In the present investigation a gypsum-bonded investment is presented with negligible setting expansion and a thermal expansion of 1. 7%. This investment can and should be used without a steel casting ring. In combination with an earlier described die-spacing technique the new investment facilitates the production of gold inlays and crowns which, independent of type, will show suitable degree of loose-fit in or in the preparations in the patient's mouth.     

Surface roughness of gold alloy castings

The present investigation has shown that the surface of gold alloys cast in both a new and probably improved investment and in two commercial gypsum-bonded investments fulfills all conventional clinical requirements as regards retention and precision of the cemented restorations and easy polish ability. With a view to retention the sometimes slightly rougher surfaces of castings in the new investment are advantageous.     

The age of restorations in situ

Jokstad A, Mjor IA, Qvist V. The age of restorations in situ. Acta Odontol Scand 1994;52:234–242. Oslo. ISSN 0001-6357.

In a cross-sectional survey the age of restorations in situ was recorded in three patient groups. Group A were randomly examined regular attenders, group B were irregular attenders randomly chosen from patient treatment records, and in group C the age of posterior gold and composite resin restorations was recorded in selected regular attenders. The study material included 8310 restorations in group A, 1281 in group B, and 500 restorations in group C. The three materials amalgam, composite, and gold accounted for more than 90% of all restorations. In group A 3.3% of the restorations were scheduled for replacement. The most prevalent reasons for replacement were secondary canes, bulk fractures of the restoration, and tooth fractures. The median age of the failed restorations was fairly similar to the median age of the acceptable restorations in situ among the regular patients (group A). The data indicate median ages of 20 years for gold restorations, 12–14 years for amalgam restorations, and 7–8 years for composite resin restorations. The restoration ages were influenced by the type and size of the restoration, the restorative material used, and possibly also the intraoral location of the restorations.     

Dental materials for posterior restorations

Abstract Assessment of the quality of dental restorations by the Ryge system is described. Generally, the quality of dental restorations is shown to be dependent on the technique sensitivity of the restorative material as well as the skill and experience of the dentist. Concerning biocompatibility, adverse reactions related to amalgam restorations are unlikely or scarce, due to small amounts of released mercury. Resin based restorative materials contain a large number of organic compounds and, as such, the toxic and allergenic potentials are unknown. Gold and ceramics turn out to be the most biotolerable dental materials. Based on studies on longevity, data indicate that the median age of amalgam restorations is 10-12 years, of gold castings 13-14 years and more, and of composite restorations 4 years. Data on longevity of ceramic restorations are sparse. Secondary caries appears to be the most frequent cause for replacement of the different restorations, followed by marginal degradation. Secondary caries account for more failures among the resin based restorations than among amalgam. Reviewing the literature, it appears that amalgam is the best and most economic dental material for routine posterior restorations with reasonable durability. Gold is recommended for complex restorations. Resin based composites may be limited to small restorations where cosmetics is the main aspect, as wear and recurrent caries are main problems. Ceramic restorations comprise aesthetic restorations with excellent bio-compatibility, however, data on longevity and marginal adaptation are not encouraging.     

Teaching of all-ceramic restorations in central European dental schools: a survey

The teaching of all-ceramic restorations in Central European dental schools in the mid 1990s has been surveyed. Based on a 65% response, the findings indicate that the majority of undergraduate (pre-doctoral) students receive instruction in all-ceramic restorations with >75% gaining clinical experience in the use of such restorations prior to graduation. When clinical experience was not received, formal instruction, either in the regular curriculum or in elective studies was generally available. All the schools, with one exception, anticipated that the importance of teaching all-ceramic restorations would increase or at least stay the same. In general, the findings were similar to those reported in studies of the teaching of all-ceramic restorations in North America, Scandinavia, and the UK and Ireland, especially in relation to luting systems, contraindications and finishing instrumentation. However, clinical requirements for all-ceramic restorations in Central European dental schools were more common than in dental schools in North America, Scandinavia and the UK and Ireland.     

包埋料和热处理对自研贵金属合金铸造适合性的影响

目的　比较不同包埋料和热处理方法对牙科铸造贵金属合金BS 1金合金铸件铸造适合性的影响。方法　采用 2种包埋料 (F 1和Z 1包埋料 )包埋模拟后牙冠的帽状代型蜡型 ,用BS 1金合金铸造 ,铸件经过不同的热处理 (软化热处理 ,硬化热处理和恒温时效硬化热处理 )后试合于各自的石膏代型 ,在体视显微镜和金相显微镜下分别测试铸件的边缘适合性和组织面密合度 ,求各自的平均值 ,统计分析各组之间的统计学差异性。结果　F 1包埋料组的边缘差异明显小于Z 1包埋料组 (P <0 0 5 )。热处理对金合金铸件的铸造适合性无显著性影响。结论　BS 1金合金用F 1包埋料包埋铸造的铸件其铸造适合性优于Z 1包埋料组。热处理对其铸造适合性无显著性影响     

包埋料和铸造方法对自研贵金属合金铸流率的影响

目的：本研究分别对Au50-Ag27-Cu14X多元贵金属合金（BS－1金合金）Ag-In 合金（BS－1银合金）的铸流率进行研究测试，从而了解包埋料和铸造方法对2种合金的铸流率和铸造边缘完整性的影响。方法：采用网状试件，测试合金的铸流率（Cv)值，比较2种包埋料（F－1和Z－1包埋料）和2种铸造方法（中频离心铸造和空气－煤气离心铸造）分别对2种合金铸流率的影响，另外，采用帽状试件判断合金铸造边缘完整性。结果：网状试件铸造结果显示，F－1和Z－1包埋料对BS－1银合金的铸流率的影响在统计学上无显著性差异（P＞0．05），其Cv值均大于95％，2种铸造方法对其铸流率也无显著性影响（P＞0．05），帽状试件结果显示，BS－1金合金和BS-1银合金的边缘较圆钝，结论：BS－1金合金和BS－1银合金具有较高的铸流率，且不受2种包埋料（F－1和Z－1包埋料）和2种铸造方法（中频离心铸造和空气－煤气离心铸造）的影响。     

Clinical short term study of marginal integrity of resin restorations

Abstract – The marginal adaptation of 649 Durafill and Silux fillings in beveled and acid etched enamel cavities was assessed in a clinical study. The investigation included Class III with and without lingual extension, Class IV and Class V. The frequency of marginal discoloration and marginal gaps after 15 months was markedly reduced in all Classes when a low-viscous resin was used prior to application of the restorative.     

The 8-year clinical performance of 15 low-gold casting alloys

The objectives of this study were to (1) evaluate the clinical performance of low-gold alloys over time, with special attention to tarnish resistance, and (2) determine the influence of compositional factors on performance. A total of 264 restorations were inserted in 50 patients using Modulay (control), Forticast, Midas, Maxigold, Midigold, Minigold, Mowrey 120, Mowrey 46, and 8 experimental alloys (UNC 1–8); 161 (61%) of the original restorations were recalled after an average of 8 years and rated for tarnish, plaque, type of material at contacts, retention of polish, surface porosity, and secondary caries. The incidence of tarnish at ranked locations was relatively low and ranged from 0.004-0.2 on a 0–2 tarnish scale. Low-gold alloys as a group were not significantly more tarnished than the control but there were differences between alloys. Palladium content appears especially important to improved tarnish resistance in alloys with very low gold content. Incidence of plaque accumulation and tarnish was highest in the proximal and cervical one thirds. There was no secondary caries and no surface porosity.     

Effect of postponed polishing on marginal adaptation of resin used with dentin-bonding agent

Abstract – Dentin cavities, prepared in extracted human teeth, were treated with two different dentin-bonding agents and filled with a light-activated microfilled resin. The maximum width of the contraction gap (MG) and the extent of the gap (GP) were then measured, using a light microscope, approximately 0.1 mm below the original free surface of the filling. The contraction gap was measured 30 s, 10 min or 60 min, and remeasured 65 min, after stop of irradiation. A positive correlation was found between the two variables, MG and GP. The product of MG and GP was chosen as basis for the statistical analyses. This "marginal index" was significantly reduced when polishing of the marginal area was postponed for 10 min with one of the dentinbonding agents and for 60 min with the other. Even though the improvement in marginal adaptation was statistically significant, this improvement was considered clinically irrelevant, It is concluded that polishing of the marginal area should not be done before the hygroscopic expansion of the resin restoration has closed the contraction gap.     

Abrasion of Class 1 restorative resins

Abstract— Studies have been made on the abrasion by food of different restorative resins in standard Class 1 cavities in mandibular first molars of schoolchildren. The abrasion was recorded by measuring the increasing height of the exposed cavity walls. It was found that Sevriton Simplified® was abraded more than Adaptic®, that no difference in abrasion between Adaptic and Adaptic without filler could be demonstrated, and that Adaptic was abraded more than an experimental composite containing 30% by weight Aerosil®, an ultra-fine SiO₂, filler with a grain size of the order of 25–50 nm. The results are in accord with the findings in an initial study by one of the present authors, in which the fillings were placed in denture porcelain teeth. It is stressed that the conclusions of the present work are pertinent only to the type of abrasion studied, i.e. chewing of food without the possibility of direct contact between the fillings involved and the corresponding antagonists.     

Effect of Gluma in acid-etched dentin cavities

Abstract – The marginal adaptation of a restorative resin in combination with a dentin bonding agent was investigated in dentin cavities treated either with a strong solution of phosphoric acid or with an 0.5 M EDTA solution neutralized to pH 7.4 with NaOH. It was found that both the maximum marginal contraction gap and the extent of the gap were significantly increased in acid-etched cavities when compared to cavities cleaned with the EDTA solution.     

Bonding of restorative resins to dentin by means of methacryloylchloride and methacryloyl-R-isocyanate

Abstract – The bonding of restorative resins to dentin by means of an intermediary monomer containing a carboxylic acid chloride or an isocyanate group was investigated. Such intermediary monomers are supposed to react with the organic constituent of dentin. Bond strengths were enhanced by the use of the intermediary monomers, resulting in mean bond strengths of 0.13 kg/mm2. Bond strengths of this order of size are probably too low to be of clinical interest.     

Correlation between tensile and bond strength of composite resins

The purpose of the present work was to measure the bond strength of five composite resins (two microfilled and three conventional) to human etched enamel and to correlate the findings with previously published results on the tensile strength of the same resins. The two microfilled composites showed a significantly lower bond strength than the three conventional products. The coefficient of correlation between tensile and bond strength was 0.74.     

A 24-month evaluation of amalgam and resin-based composite restorations: Findings from The National Dental Practice-Based Research Network

BackgroundKnowing which factors influence restoration longevity can help clinicians make sound treatment decisions. The authors analyzed data from The National Dental Practice-Based Research Network to identify predictors of early failures of amalgam and resin-based composite (RBC) restorations.MethodsIn this prospective cohort study, the authors gathered information from clinicians and offices participating in the network. Clinicians completed a baseline data collection form at the time of restoration placement and annually thereafter. Data collected included patient factors, practice factors and dentist factors, and the authors analyzed them by using mixed-model logistic regression.ResultsA total of 226 practitioners followed up 6,218 direct restorations in 3,855 patients; 386 restorations failed (6.2 percent) during the mean (standard deviation) follow-up of 23.7 (8.8) months. The number of tooth surfaces restored at baseline helped predict subsequent restoration failure; restorations with four or more restored surfaces were more than four times more likely to fail. Restorative material was not associated significantly with longevity; neither was tooth type. Older patient age was associated highly with failure (P N/A .001). The failure rate for children was 4 percent, compared with 10 percent for people 65 years or older. Dentist’s sex and practice workload were associated significantly with restoration longevity.ConclusionsIn this prospective cohort study, these factors were significantly predictive of failure for amalgam and RBC restorations: patient’s age, a higher number of surfaces restored at baseline, the dentist’s sex and the practice workload. Material choice was not significantly predictive in these early results.Practical ImplicationsIf clinicians can recognize and identify the risk factors associated with early restoration failure, more effective treatment plans may be offered to the patient.