The clinical performance of laboratory-fabricated crowns placed on first permanent molars with developmental defects

BACKGROUND: Young permanent molars with developmental enamel defects commonly are treated with stainless steel crowns. However, allergic reactions to nickel and chromium have been reported by some patients. The literature contains no evaluations of alternative treatments. METHODS: In a retrospective study, the authors evaluated the clinical performance of cast gold crowns and tooth-colored composite or ceramic crowns placed on first permanent molars with developmental defects in children 6 to 8 years of age. A total of 41 molars were prepared. After crown preparation, an impression was made, and crowns of cast gold, Artglass (J.F. Jelenko & Co.) composite or Empress (Ivoclar) leucite-containing ceramic were fabricated and clinically evaluated every six months for a period ranging from two to five years postoperatively (mean three years). RESULTS: After two to five years, all crowns were fully retained. The marginal adaptation of 39 of the 41 crowns was rated excellent, and the marginal adaptation of the remaining two crowns (both gold) received acceptable ratings. In two cast gold crowns, the margins were subgingival at cementation; the remaining 39 crowns had supragingival margins at the time of luting. By the end of the second year, all margins were supragingival. All teeth were vital and asymptomatic at all evaluation points. No secondary caries was recorded. Neither gingival inflammation nor loss of vertical dimension was recorded in any case. All crowns were well-accepted by the patients and their parents. CONCLUSIONS: Laboratory-fabricated crowns can be used for the treatment of young permanent molars with developmental defects. CLINICAL IMPLICATIONS: Cast gold, composite or ceramic crowns can be used successfully to treat developmental defects of first permanent molars in children.     

Influence of recasting palladium-silver alloy on the fit of crowns with different marginal configurations

STATEMENT OF PROBLEM: Dental laboratories may occasionally recast previously cast dental alloy to produce a prosthesis, but this process may have a negative influence on marginal adaptation. PURPOSE: The aim of this study was to evaluate the cervical and internal fit of complete metal crowns that were cast and recast using palladium-silver alloy and 3 different marginal configurations: straight shoulder, 20-degree bevel shoulder, and 45-degree chamfer. MATERIAL AND METHODS: Thirty aluminum dies were made, 10 for each marginal configuration. Each group of 10 was further divided into 2 subgroups (n=5), according to the alloy (Pors-on 4) casting history. The dies were waxed using a cylindrical metal matrix to standardize the thickness of the walls. The wax patterns were invested in a phosphate-bonded investment (Deguvest) and cast after heating in an oven (EDG), according to the manufacturer's instruction. The alloy was melted with an oxygen-gas heat source and cooled to room temperature after casting. Afterwards, the specimens were seated on the dies with a static load of 9 kgf for 1 minute. The marginal discrepancy was measured with a metric microscope, using a digital micrometer. All the measurements were done by the same operator. Each crown-die interface was measured 3 times on each of the 4 diametrically opposite points, for a total of 12 measurements for each specimen. Specimens were longitudinally sectioned to obtain 2 hemi-sections for internal discrepancy measurements, measured at 3 points: 1 in the center of the occlusal wall and 2 at each center of each axial wall. Three measurements were made for each point, for a total of 9 measurements per specimen. The results were submitted to parametric statistical 3-way analysis of variance followed by Tukey-Kramer HSD post hoc analysis (alpha=.05). RESULTS: The new alloy provided significantly better adaptation (P<.001) than the recast alloy for both marginal and internal discrepancy measurements. Marginal designs did not shown any statistical differences when the new metal was used. For recast metal, the straight shoulder showed significantly better adaptation (P<.001) than the 20-degree bevel shoulder and the 45-degree chamfered configurations, which were statistically similar to each other. CONCLUSION: The results of this study suggest that recasting procedures for crown fabrication should not be used with the palladium-silver alloy tested.     

Marginal adaptation and micro-porosity of class II restorations of a high copper amalgam and a palladium-free gallium-based alloy

The aim of the current investigation was to compare the marginal adaptation and internal porosity of a gallium (Ga)-based alloy (Galloy) with a high copper amalgam (Permite C DP) when used in moderately sized conventional class II cavities. Ten dentists placed two restorations of each material in standardized class II cavities in typodont teeth set in a phantom head. The proximal surfaces of the restored teeth were subsequently examined using an optical microscope and colour photographs were taken. The teeth were then serially sectioned before being re-examined microscopically and re-photographed. Three dentists rated the photographs of the restorations on two occasions, 2 weeks apart, for marginal adaptation and internal porosity using a six and five point scoring criteria, respectively. Inter- and intra-examiner agreements were assessed with weighted kappa statistics. The Ga-based alloy exhibited inferior marginal adaptation and a significantly higher level of porosity and internal defects compared with the dental amalgam. Marginal defects were mainly concentrated at the gingival third of the proximal boxes for both alloys. The poor marginal adaptation and extensive internal porosity detected for the Ga-based alloy was attributed to the difficulty in the alloy condensation related mainly to the 'stickiness' of the alloy to the condensers and to the rapid change in the plasticity of the alloy during condensation. This could possibly be a factor in the post-operative complications reported with the clinical use of this alloy.     

Internal adaptation of cobalt-chromium posts fabricated by selective laser melting technology

Statement of problem

Selective laser melting (SLM) has become popular in prosthetic dentistry. However, only limited information is available for the internal adaptation of cobalt-chromium (Co-Cr) posts fabricated by SLM.

The tensile and shear strength of a base metal weld joint used in dentistry

Samples of a base mental alloy were cast and welded together using a conventional welding procedure. The joints were loaded and placed either in a corrosive environment or in air for varying time periods. The tensile and shear strength of the joints was unaffected by the corrosive environment, and the joints, despite some internal defects, appeared suitable for clinical use.     

3D evaluation of composite resin restoration at practical training using swept-source optical coherence tomography (SS-OCT)

Internal adaptation of restorations to the cavity wall is one of the important topics in clinical dentistry. The purpose of this study was to investigate the possibility to utilize the non-invasive tomographic imaging system for teaching the importance of cavity adaptation at dental school pre-clinical training. Swept-source optical coherence tomography (SS-OCT) was used for detection of marginal and internal defects in the composite resin restorations as an educational device. Class 1 and Class 2 composite restorations to melamine resin molar tooth were assigned to the students and prepared during the skill test, and SS-OCT imaging was performed to evaluate students' works. SS-OCT could detect the internal gaps and voids within the restorations in tomography images synthesized based on the backscatter signal from within the restoration. It is suggested that the SS-OCT is promising diagnostic modality, as well as educational imaging device for the detection of internal gaps in adhesive restorations.     

Effect of layer thickness on the marginal and internal adaptation of laser-sintered metal frameworks

Statement of problemLaser sintering is commonly used for fabricating metal-ceramic restorations. The layer thickness of the sintering process may affect restoration adaptation. However, limited information is available regarding its impact.PurposeThe purpose of this in vitro study was to compare the marginal and internal adaptation of laser-sintered cobalt-chromium single crown frameworks sintered with layer thicknesses of 25 and 50 μm.Material and methodsThirty resin dies that represented prepared single molar abutment teeth were prepared by using a 3-dimensional printer and were divided into 3 groups (n=10) according to the method used for fabricating metal frameworks: group C, metal frameworks fabricated by using the lost-wax method (control); group L25, metal frameworks fabricated by using direct metal laser melting with a layer thickness of 25 μm; and group L50, metal frameworks fabricated by using direct metal laser melting with a layer thickness of 50 μm. After fabricating the metal frameworks, 15 vertical marginal discrepancy measurements were made in each axial region (mesial, distal, buccal, and lingual) using a stereomicroscope. Next, all the specimens were sectioned from the midline, and 5 internal discrepancy measurements were made in each internal region (inner marginal, axial, and occlusal). The data were analyzed statistically by using 1-way ANOVA, the Tukey honestly significant difference, and Tamhane T2 tests (α=.05).ResultsThe highest marginal and internal discrepancy values were obtained for metal frameworks in group C, and these values were significantly different (P<.001) from those obtained for metal frameworks in the other 2 groups. No significant difference was observed in the marginal and internal discrepancy values of metal frameworks in groups L25 and L50.ConclusionsThese results indicate that layer thickness does not affect the adaptation of laser-sintered metal frameworks, yet both sintering parameters yielded significantly lower mean marginal discrepancy values than the cast group.     

Prefabricated Stock Trays for Impression of Auricular Region

The conventional methods of impression making for maxillofacial defects are cumbersome and time consuming for both patient and operator. This study focuses upon standardizing and simplifying the impression making methodology for auricular prosthesis with the help of prefabricated stock trays for auricular region. The stock trays were designed on positive replicas of anatomical structures, broadly divided into long and narrow, short and broad and long and broad ear. For each stock tray, impressions of auricle, of patients of different morphology were made with plastic funnels of different shape and size ensuring at least 6 mm of space between the anatomical part and inner surface of funnel and master cast was obtained. Subsequent adaptation of wax was done and fabrications of stock stainless steel trays were done. A standardized stock tray for making of auricular impressions was developed. From this innovative technical procedure it is possible to get an accurate impression of auricular defects now by the use of prefabricated stock trays rather than the cumbersome conventional method.     

使用FUS-invest锆系牙科纯钛包埋料提高铸件的物理机械性能及精度

目的:评价自制FUS-invest锆系牙科纯钛包埋料铸造的纯钛铸件的物理机械性能及标准化单冠的精度.方法:制备7个厚度为0.8 mm的纯钛比例铸件.经伺服液压动态实验系统、断口扫描电镜观察及能谱分析,评价其物理机械性能.制备38个标准化单冠,实验组(FUS-invest锆系包埋料)、对照组(磷酸盐系包埋料)各19个,测量显微镜测标准化单冠边缘差异值d和铸件内壁与工作模的距离,进行铸件精度评价.采用SPSS17.0软件包对数据进行统计学分析.结果:①纯钛铸件的弹性模量为(123.5±14.2)GPa,屈服强度为(569.3±16.5) MPa,抗拉强度为(668.4±16.1) MPa,延伸率为(4.5±0.2)％;断口EDS分析除钛元素外,不同深度处可发现少量不同含量的Si元素和Fe元素,但未检测出Zr元素.②精度实验中,单因素方差分析及两独立样本t检验显示,组内标准化单冠边缘4个标记点处的测量值无显著差异(P＞0.05);实验组和对照组相比亦无显著差异(P＞0.05).2组内部测量值无显著差异(P＞0.05),而组内内部不同标记点间差异显著(P＜0.01).结论:虽然FUS-invest锆系包埋料铸造获得铸件的延伸率略低,但各项物理机械性能均达到临床要求.无论边缘适合性还是内部适合性,2组均无显著差异且均在临床可接受范围,2组边缘差异均值约为46 μm,内部近咬合面的差异均值约为56 μm,内部轴壁处的差异均值约为0.     

Improving the adaptation of denture bases by anchorage to the casts: a comparative study

The purpose of this study was to investigate the adaptation of complete maxillary dentures to stone casts processed by the conventional, and two anchoring, methods. The anchoring methods used holes drilled on the cast and a special flange extended onto the posterior aspect of the maxillary cast. Both anchoring methods improved the adaptation of denture bases by minimizing the discrepancy between the denture base and cast. The greatest discrepancies observed in all methods were at the central portion of the posterior border.     

Accuracy of adaptation of thermoformed poly(methyl methacrylate)

Thermoformed poly(methyl methacrylate) (PMMA) sheet is used to produce a number of different dental appliances such as stents, occlusal splints and baseplates for occlusal rims. The purpose of the present study was to measure the accuracy of adaptation of Perspex PMMA sheet and to determine the effect of annealing on the accuracy of the thermoformed specimens. The results of the study showed that PMMA can produce specimens that are accurately adapted to the cast. Immersion in water resulted in an increase in the space between the cast and the specimen for both thermoformed and thermoformed and annealed acrylic resin. Annealing of the thermoformed specimens had significantly less increase in space between the cast and the specimens when immersed in water over a period of 3 months.     

Intermittent loading of teeth with tapered, individually cast or prefabricated, parallel-sided posts.

This study compared the resistance to intermittent loading of teeth with tapered, individually cast posts and cores or prefabricated parallel-sided posts (Para-Post, Whaledent) and composite cores. Bovine teeth mounted in acrylic resin blocks with a simulated periodontium were used for the study. Two conditions were studied. One group received individually fabricated posts and cores, the second had titanium prefabricated posts and resin composite cores placed. All teeth receiving posts and cores had cast crown restorations placed. Teeth were intermittently loaded using a force of 250 N twice each second at an angle 45 degrees to the long axis until failure occurred. Teeth with prefabricated posts and resin composite cores showed a significantly higher resistance to intermittent loading than did teeth with tapered, individually cast posts and cores. Additional restored teeth were sectioned and the adaptation of the posts to the root were measured. The adaptation of the prefabricated posts was better than that of tapered, individually cast posts.     

Comparison of the adaptation of acrylic resin cured by microwave energy and conventional water bath

Acrylic resin record bases made from three commercial resins were processed by water bath curing and by microwave energy. The adaptation of the record bases to a standard cast was measured to determine if there were any statistically significant differences in the fit that could be attributed to the differences in curing methods and the brands of resin. The results indicated a small statistically significant difference in favor of the water bath cure overall, but clinically there were no appreciable differences in the adaptation of the record bases with either curing method or the resins used. The adaptation of artificial dentures made from acrylic resin is clinically acceptable with either microwave curing or the water bath method.     

Adaptation of acrylic dentures reinforced with metal wire

The aim of this study was to reveal the effect of metal wire on the adaptation of the denture reinforced with it. Forty maxillary dentures were made with two polymerization systems (DS system and SR-Ivocap system). The dentures were divided into two groups: (1) the unreinforced dentures (control) and (2) the dentures reinforced with metal wire 1.0 mm in diameter. Discrepancies between the denture base and the stone cast were measured at five points immediately after polymerization and after a 30-day immersion in water. The data were analysed using a two-way or one-way ANOVA test. Dentures reinforced with metal wire exhibited significantly lower adaptation to the stone cast than the unreinforced ones for each polymerization system. Immersion in water did not affect the adaptation of dentures reinforced with metal wire for each polymerization. Unreinforced dentures made by the DS system had significantly smaller discrepancies compared with the dentures processed with the SR-Ivocap system. The adaptation of the dentures reinforced with metal wire decreased in comparison with the unreinforced ones regardless of the polymerization method. This should be considered when metal wire is used clinically as reinforcement.     

Clinical-epidemiological analysis of the results of treatment by non-removable constructions in patients with partial absence of teeth

In representative clinical-epidemiological study of the results of treatment of the patients with embraced defects of dentitions with non-removable bridge-like constructions having intermediate part of 1 to 3 artificial crowns has revealed risk profiles of complications and defects. It is shown that cumulative portion of complications by remote results for 10-year period reaches 33% for punched-soldered dentures and 10%--for cast dentures. Models of the type of "tree of decisions" for prognosis of non-removable bridge-like dentures are proposed.     

A simplified palatal expansion prosthesis

A palatal expansion prosthesis made of cast silver can be easily fabricated at any facility that has the ability to cast type III gold. The ductility and malleability of pure silver allow for ease of adaptation or alteration as a chairside or operating room procedure.     

Comparison of internal escape channels with die spacing and occlusal venting

The effectiveness of the following procedures in improving the seating of full cast crowns were compared: internal escape channels, die spacing, occlusal venting, and a combination of die spacing with an escape channel. All techniques were shown to be similar in effectiveness. Die spacing produced the least consistent results. An internal escape channel, occlusal venting, die spacing, or a combination of an escape channel and die spacing did not influence the retention of full cast crowns.     

Radiographic evaluation of 12% Au-Ag-Pd alloy cast lower denture plates constructed by dental student as a laboratory exercise

We evaluated 12% Au-Ag-Pd alloy cast lower denture plates prepared by dental students in laboratory exercises for casting defects. First, we determined the most suitable exposure conditions for nondestructive radiographic test of 12% Au-Ag-Pd alloy. Subsequently, 130 plates were nondestructively evaluated by radiography under the most suitable exposure conditions. In radiographic testing using X-Omat RP films (Eastman Kodak Co.) and X-Omatic Fine Screen (Eastman Kodak Co.), the most suitable exposure conditions involved a target-to-film distance of 1.9 m, tube voltage of 148 Kvp, tube current of 10 mA, and exposure time of 1.5 sec. Preliminary radiographic examination of artificial casting defects revealed semispherical defects in the diameter of 0.25 mm in 1.6 mm-thick 12% Au-Ag-Pd alloy plates and detects of 0.26 mm in 2.4 mm thick plates. In the 130 cast plates, 56 casting defects were detected. These defects were found at the left webbing part in 40 (30.8%), right webbing part in 36 (27.7%), lingual bar in 7 (5.4%), I-bar in 4 (3.0%), and at other regions of the metal frames in 3 (2.3%) cases. These results indicate that nondestructive radiographic testing is as effective in detection of casting defects in 12% Au-Ag-Pd alloy cast plates as it is in Co-Cr and Ni-Cr alloy plates. This method was also found to be effective in evaluation of the practice metal frames constructed by dental students.     

直接法与间接法分瓣桩核冠修复磨牙的临床观察

目的:观察直接法与间接法制作分瓣桩核冠修复严重缺损磨牙的临床效果。方法:对42颗经过完善根管充填后的严重缺损的磨牙,19颗行间接法制作分瓣桩冠修复,23颗行直接法制作分瓣桩核修复,并随访3年。结果:两组桩核冠修复的临床效果无显著性差异(P>0.05)。结论:直接法与间接法制作分瓣桩核冠修复严重缺损磨牙均可取得良好的临床效果。     

Marginal and internal adaptation of class II restorations after immediate or delayed composite placement

Direct class II composite restorations still represent a challenge, particularly when proximal limits extend below the CEJ. The aim of this in vitro study was to evaluate the influence of the type of adhesive and the delay between adhesive placement and composite insertion on restoration adaptation. Direct class II MOD box-shaped composite restorations (n=8 per group) were placed on intact human third molars, with proximal margins 1mm above or under CEJ. All cavities were filled with a horizontal layering technique, immediately after adhesive placement (IP) or after a 24h delay (DP). A filled three-component adhesive (OptiBond FL: OB) and a single-bottle, unfilled one (Prime & Bond 2.1: PB) were tested. Marginal adaptation was assessed before and after each phase of mechanical loading (250000 cycles at 50 N, 250000 cycles at 75 N and 500000 cycles at 100 N); internal adaptation was evaluated after test completion. Gold-plated resin replicas were observed in the SEM and restoration quality evaluated in percentages of continuity (C) at the margins and within the internal interface, after sample section. Adaptation to beveled enamel proved satisfactory in all groups. After loading, adaptation to gingival dentin degraded more in PB-IP (C=55.1%) than PB-DP (C=86.9%) or OB-DP (C=89%). More internal defects were observed in PB samples (IP: C=79.2% and DP: C=86.3%) compared to OB samples (IP: C=97.4% and DP: C=98.3%). The filled adhesive (OB) produced a better adaptation than the 'one-bottle' brand (PB), hypothetically by forming a stress-absorbing layer, limiting the development of adhesive failures. Postponing occlusal loading (such as the indirect approach) improved also restoration adaptation.