Clinical evaluation of the marginal fit of cast crowns – validation of the silicone replica method

Summary  Replication of the space between a tooth and its cast crown, using a light-body silicone supported by a heavy-body silicone, is a recognized technique to evaluate the quality of a restoration. This study validates a similar method that is of great clinical and experimental interest. Whatever the type of silicone used, comparison is possible between different technical procedures of crown elaboration (type of impression, type of material, method of spacing, etc.). If an appropriate silicone is used, the cement space may be reproduced and its thickness measured, whatever the localization (cervical, axial, occlusal).     

A clinical evaluation of the agar alginate combined impression: dimensional accuracy of dies by new master crown technique

PURPOSE: To evaluate the dimensional accuracy of several impression methods including agar alginate combined impression in vivo; the marginal accuracy of stone dies was determined using a new electroformed master crown technique. MATERIALS AND METHODS: Cast cores with knife-edge and chamfer margins and electroformed master crowns were fabricated for 3 patients. Five impressions were taken of each preparation, using agar alginate combined impression and silicone impression materials. Dies were made after impression. The marginal fit of the master crown on each die was analyzed by four-way analysis of variance (ANOVA) and Tukey HSD test (p<0.05). RESULTS: The marginal fit of the master crown on the dies with chamfer margin was better than those with knife-edge margin for agar alginate combined impression. The shape of the margin did not affect the accuracy when silicone impression material was used. CONCLUSIONS: The results suggest that the agar alginate impression method is clinically acceptable for the chamfer margin, but shape of the margin may affect the dimensional accuracy of dies. The shape of the margin does not affect the accuracy of dies when silicone impression was used. Furthermore, the master crown made by electroforming technique could be useful for clinical evaluation of impression methods.     

An innovative method for evaluation of the 3-D internal fit of CAD/CAM crowns fabricated after direct optical versus indirect laser scan digitizing

PURPOSE: A procedure for 3-D analysis of the internal fit of fixed restorations has been developed. This study tested this method for investigating the fit of all-ceramic crowns. MATERIALS AND METHODS: Twelve data sets of a prepared maxillary canine were acquired by direct digitizing of the metal master die (CEREC 3 camera) and by digitizing gypsum dies after conventional impression taking (CEREC 3 scan), respectively. Using these data sets, 24 all-ceramic single crowns each were machined out of two glass-ceramics. The method is based on duplicated gypsum dies of the metal master, which were made for each crown. The space between the duplicate die and the internal surface of the respective crown was filled with a low-viscosity addition silicone. These silicone films (replicas) and their corresponding dies were digitized in the same measuring position. The internal fit was calculated and quantitatively and qualitatively analyzed. RESULTS: The mean and maximum positive deviations were 348 microm and 986 microm (camera), respectively, and 294 microm and 830 microm (scan), respectively, for Vitablocs Mk II and 332 microm and 920 microm (camera), respectively, and 307 microm and 852 microm (scan), respectively, for ProCAD. For both systems, the deviations were highest at the edges. CEREC scan yielded significantly better internal fit accuracy compared to the CEREC camera. CONCLUSION: Evaluation of the internal 3-D fit using the innovative method proved to be suitable. Indirect data acquisition using impression taking showed improved internal fit compared with the direct procedure. However, the differences between the data-acquisition techniques are small compared to their absolute values.     

Clinical fit of Procera AllCeram crowns

STATEMENT OF PROBLEM: Color stability, strength, and accuracy of fit are the main requirements for complete-ceramic crowns. The Procera AllCeram crown system is a CAD/CAM system used to fabricate individual complete-ceramic crowns that have a dry sintered, aluminum oxide core and appear to match clinical requirements. However, there are few articles about the clinical fit of all-ceramic crowns. PURPOSE: This in vivo study measured the accuracy of fit of Procera AllCeram crowns in anterior and posterior teeth. MATERIAL AND METHODS: The clinical fit of 80 anterior and posterior Procera AllCeram crowns was evaluated by a replica technique with a light body silicone to fill space between crown and tooth and a heavy body silicone to stabilize the light body film. After removal from the artificial crowns, the replicas were segmented, and measurements of the film thickness were performed with a light microscope. RESULTS: Medians of mean marginal gap widths were between 80 and 95 microm in anterior teeth and between 90 and 145 microm in posterior teeth. Medians of maximal marginal gap widths ranged from 80 to 180 microm in anterior teeth and from 115 to 245 microm in posterior teeth. CONCLUSION: The accuracy of fit achieved by Procera AllCeram was comparable to other conventional and innovative systems.     

Suitability of the triple-scan method with a dental laboratory scanner to assess the 3D adaptation of zirconia crowns

Statement of problemThe triple-scan method for assessing the 3D adaptation of dental restorations has been introduced and reported to be reliable. However, the suitability of using a dental laboratory scanner in the triple-scan method has not been evaluated.PurposeThe purpose of this in vitro study was to evaluate the suitability of the triple-scan method using a dental laboratory scanner to assess the 3D adaptation zirconia crowns.Material and methodsA zirconia abutment and a zirconia crown were fabricated, and the abutment was fixed in a custom-made base. The crown was seated onto the abutment with the interposition of light-body silicone impression material between them. The triple-scan method was performed by using a dental laboratory scanner, and the mean cement-gap thickness was calculated. The seating and digitalization process was repeated 10 times, and after each digitalization, the light-body silicone layer was stabilized by applying heavy-body silicone impression material over it. Cement-gap thickness was measured on cross-sections of the aligned scan data sets and of the physical silicone replica. The results were assessed by using the paired t test and the Bland-Altman method (α=.05).ResultsMean 3D cement-gap thickness assessed by the triple-scan method reported small dispersion with a coefficient of variation of 5.6% for the occlusal area, 1.9% for the axial area, and 6.4% for the margin area. Cement gap thickness measured at corresponding locations in the aligned scan data sets and in the physical silicone replica reported no significant difference (P=.326) and good agreement.ConclusionsThe cement gap was accurately duplicated in scan data sets. The triple-scan method by using a dental laboratory scanner is suitable for assessing the 3D adaptation of zirconia crowns.     

Influence of investment type and sprue number on the casting accuracy of titanium crown margins

STATEMENT OF PROBLEM: Titanium offers biocompatibility and adequate mechanical properties for fabricating dental prostheses; however, casting difficulties can compromise the accuracy of titanium crown margins. PURPOSE: The aim of this study was to evaluate the influence of investment type and number of sprues on accuracy of crown castings made with commercially pure titanium. MATERIAL AND METHODS: The casting accuracy was evaluated indirectly by determining the deficiency of titanium crown margins cast using the lost-wax technique. Crown margins were recorded in a silicone impression material. The degree of marginal rounding was measured and margin deficiencies were calculated. Seventy-five acrylic resin crown patterns with wax margins were prepared on a stainless steel stylized crown die having a 30-degree beveled finish line. Fifteen patterns were selected for the control group, and the degree of wax margin rounding was determined (group W, control). The remaining 60 were divided into 4 groups of 15 each, and cast using 2 different titanium investments: a monoammonium dihydrogenphosphate-bonded investment (Rematitan Plus; groups PI and PII), and a magnesium oxide-bonded investment (Rematitan Ultra; groups UI and UII). Each pattern was cast with either 1 (groups PI and UI) or 2 (groups PII and UII) sprues. Margin configurations for both wax pattern and cast specimens were measured and recorded with the same method, using silicone impressions of the margins. After polymerization, the silicone material was sectioned precisely in 8 locations through the margin area so that cross-sections of the margins could be observed. Marginal deficiency was determined using microscopic measurements from the silicone patterns and calculations. Data were subjected to 2-way analysis of variance (alpha=.05). RESULTS: Specimens from group W presented a mean marginal deficiency of 19 +/- 6 microm. The analysis of variance indicated a significant difference for the main factors, investment (P<.01) (P=91 +/- 28 microm and U=78 +/- 17 microm) and sprue number (P<.001) (I=97 +/- 23 microm and II=72 +/- 16 microm), as well as for interaction (P<.05) (PI=109 +/- 25 microm; PII=73 +/- 17 microm; UI=85 +/- 15 microm; and UII=71 +/- 16 microm). CONCLUSION: Within the limitations of this study, investment U provided better casting accuracy than investment P. Two sprues provided more accurate results than 1 sprue; however, this effect was more notable for investment P, as it produced similar results between groups PII and UII.     

Fit of electroformed porcelain-fused-to-metal crown on implant abutment

This study compared the adaptation of a conventional and an electroformed porcelain-fused-to-metal crown. A master model was selected from an ITI implant with a solid abutment (height: 4 mm). Conventional cast metal frameworks of 0.7 mm thickness were prepared with a high noble metal alloy (Degudent U, Degussa) for porcelain fusing (n = 5). Electroformed frameworks of 0.2 mm thickness were determined using pure gold deposition on the abutment using the Auro-Galva-Crown system (AGC, Wieland) (n = 5). Subsequently, a porcelain (Super Porcelain AAA, Noritake) was fused to each framework. Internal gaps between the framework and its abutment were determined using the thickness of a silicone fit checking material. The gaps were measured both before and after porcelain fusing. The thicknesses of the silicone layer of the electroformed and the conventional porcelain-fused-to-metal crown were 34.6 and 38.5 microns at the margin, 33.2 and 39.6 microns at the internal slope, 22.0 and 33.0 microns at the axial, 58.6 and 65.1 microns at the occlusal, respectively. Three-way analysis of variance revealed that the mean gaps in the electroformed porcelain-fused-to-metal crown were significantly thinner than those in the conventional porcelain-fused-to-metal crown (p < 0.05). The electroformed porcelain-fused-to-metal crown showed better adaptability than the conventional porcelain-fused-to-metal crown regardless of porcelain fusing.     

The castability of pure titanium compared with Ni-Cr and Ni-Cr-Be alloys

STATEMENT OF PROBLEM: Titanium is the most biocompatible metal available for dental casting; however, there is great concern about its castability since this aspect of a casting metal/alloy has direct influence on the marginal fit of dental crowns. PURPOSE: The purpose of this study was to compare the castability of commercially pure titanium with 2 Ni-Cr base metal alloys. MATERIAL AND METHODS: Castability was evaluated indirectly by determining the sharpness of cast crown margins using the lost-wax technique. Castability was expressed in terms of the deficiency (mum) between an actual casting margin and a potentially perfect margin. Crown margins were recorded in a silicone impression material. The degree of marginal rounding was measured and margin length deficiencies (mum) were calculated. Sixty acrylic resin crown patterns with wax margins were prepared on a stainless steel stylized crown die having a 30-degree beveled finish line. The degree of wax margin rounding was determined in the control group (group W, n=15). The remaining 45 crown patterns were divided into 3 groups (n=15) and cast in commercially pure titanium (Tritan, group Ti), Ni-Cr-Be alloy (Verabond; group VB), and Ni-Cr alloy (Verabond II; group VBII). Margin configurations for both wax patterns and cast specimens were measured and recorded with the same method, using silicone impressions of the margins. After polymerization, the silicone material was sectioned in 8 locations through the margin area so that cross sections of the margins could be observed. Marginal deficiency was determined using microscopic measurements from the silicone sections and calculations. Data were subjected to 1-way ANOVA and Tukey HSD test (alpha=.05). RESULTS: Statistical analysis showed significant differences among the groups W, Ti, VB, and VBII (P<.001). The Tukey test revealed that Ti (108 +/-26 microm) was not significantly different from VBII (95 +/-35 microm), but was significantly different than Groups VB (22 +/-5 microm) and W (19 +/-6 microm), which were similar. CONCLUSIONS: Within the limitations of this study, the castability of titanium was poor compared to Ni-Cr-Be alloy, but similar to Ni-Cr alloy.     

In vitro evaluation of the "replica technique" in the measurement of the fit of Procera crowns

AIM: The objective of this study was to compare the film thickness of a light body polyvinylsiloxane addition silicone impression material using the "replica technique" (RT) to the film thickness resulting from the cementation of Procera copings. METHODS AND MATERIALS: Twenty Procera copings were fabricated on ten casts each having one central incisor and one premolar. The thickness of the light body was first measured using the RT; then on the same casts dies were cemented with glass-ionomer cement, sawed, and the film thickness of cement was measured. These two materials were expected to behave differently under stress according to their respective physical properties. RESULTS: The thickness of silicone material did not differ significantly from that of the glass-ionomer cement used in this experiment. Also, when the two groups of central incisors and premolars were taken separately, at three different areas (occlusal, axial, and cervical), no significant difference was found. Only when each surface (buccal, palatal, mesial, and distal) was compared separately at the cervical area, some significant differences between the two techniques was detected. CONCLUSION: Within the limitations of this study, the RT is an accurate and reliable technique that can simulate crown gap space after cementation. CLINICAL SIGNIFICANCE: The RT is reliable for evaluating cement thickness at the marginal and internal gaps of Procera AllCeram crowns during try-in sessions.     

New evaluation method by microfocus radiograph CT for 3D assessment of internal adaptation of all-ceramic crowns

The aim of this study was to evaluate the effectiveness of the microfocus radiograph CT system in examining the adaptation of all-ceramic crowns three-dimensionally and non-destructively. The computed tomograms of the crown and abutment model were filmed by microfocus radiograph CT. Using a volumetric rendering software, images of gaps were extracted and reconstructed three-dimensionally, and their volume data analyzed. In order to compare this method with the conventional method, fitness test silicone paste was sandwiched between the abutment and all-ceramic crown. Adaptation of the crown on the abutment model was then observed non-destructively and three-dimensionally. Furthermore, the gaps could be analyzed in any arbitrary position. Concerning mean gap thickness, there was significant differences between the two measurement methods. However, it was very slight. We therefore concluded that the microfocus radiograph CT system is well positioned to be an extremely effective method in examining the adaptation of all-ceramic crowns.     

自制硅橡胶印模材料对铸造中熔全冠适合性研究

目的:初步探讨自制国产硅橡胶印模材料对全冠的适合性。方法:将12个类复合树脂的高分子材料主模型随机分成两组,分别用国产硅橡胶和Exaflex硅橡胶两种印模材料制作SDA-Ⅱ型中熔全冠,分别在体视显微镜下测量边缘密合度情况和面浮升量。结果:国产硅橡胶组的边缘间隙(marginal open)为01102 mm?01019 mm,面浮升量(inner fit)为01091 mm?01022 mm,Exaflex的边缘间隙为01085 mm?01016 mm,面浮升量为01074 mm?01034 mm。国产硅橡胶组与Exaflex组边缘适合性和面浮升量无显著性差别(P>0105)。结论:自制硅橡胶印模材料取模制作SDA-Ⅱ型全冠的适合性在临床上可接受。     

The effect of tray selection on the accuracy of elastomeric impression materials

This study evaluated the accuracy of reproduction of stone casts made from impressions using different tray and impression materials. The tray materials used were an acrylic resin, a thermoplastic, and a plastic. The impression materials used were an additional silicone, a polyether, and a polysulfide. Impressions were made of a stainless steel master die that simulated crown preparations for a fixed partial denture and an acrylic resin model with cross-arch and anteroposterior landmarks in stainless steel that typify clinical intra-arch distances. Impressions of the fixed partial denture simulation were made with all three impression materials and all three tray types. Impressions of the cross-arch and anteroposterior landmarks were made by using all three tray types with only the addition reaction silicone impression material. Impressions were poured at 1 hour with a type IV dental stone. Data were analyzed by using ANOVA with a sample size of five. Results indicated that custom-made trays of acrylic resin and the thermoplastic material performed similarly regarding die accuracy and produced clinically acceptable casts. The stock plastic tray consistently produced casts with greater dimensional change than the two custom trays.     

CS3600■口扫数字化印模技术与传统硅橡胶印模技术在磨牙全瓷冠修复中的比较

目的:比较数字化口内直接印模技术与传统精细硅橡胶印模技术在磨牙全瓷冠修复中的效果。方法:研究选取2019年10月~2020年1月于华中科技大学同济医学院附属同济医院口腔修复科行磨牙全瓷单冠修复治疗的患者32例,共计36颗患牙。实验组18颗患牙采用CS3600^■口内扫描仪制取数字化印模,对照组18颗患牙采用传统硅橡胶印模技术制取印模。记录两组取模时间、戴牙时间及患者舒适度,修复完成2个月参照改良美国公共卫生署(USPHS)标准对修复体进行评价。结果:实验组取模时间更短、取模更舒适;制作的修复体戴牙时间更短、修复体边缘适合性更好(P<0.05)。结论:在磨牙全瓷冠的修复治疗中,CS3600^■口内扫描技术在取模时间、取模舒适度、戴牙时间和修复体边缘适合性等方面都优于传统硅橡胶印模技术。     

The method of esthetic crown restoration with composite resin jacket crown in primary molars

The term "esthetics" has recently been also used in the dental field, and a field called esthetic dentistry is increasingly being noted. The number of not only adult but also pediatric patients who visit for treatment aiming at esthetic recovery is being increased. Inpedodontics, composite resin of the coronal color is generally used in the restoration of deciduous incisors. However, the method using metal crowns for the deciduous teeth is used for the deciduous molars at present. We applied a composite resin jacket crown to the deciduous molar in a way similar to that of esthetic crown restoration for the anterior teeth. The surgical procedure before crown preparation varied slightly according to the presence or absence of pulpal treatment of vital teeth and with non-vital teeth, but the application was performed as follows: 1) Desensitization of pulp, pulpal treatment and core construction. 2) Preparation of crown. 3) Selection, trial set and occlusal equilibration of a metal crown for the deciduous tooth. 4) Precision impression with a silicone impression material. 5) Removal of the metal crown for the deciduous tooth from the impression material. 6) Making of an under-cut to the abutment tooth on the buccal lingual side. 7) Filling of the impression with chemical polymerization resin. 8) Application of pressure in the oral cavity. 9) Adjustment of edge and crown forms. Thus, the preparation method for the composite resin jacket crown was relatively simple. Since this surgery, the patient has been followed up for 1 year and 6 months, and no specifically troublesome points have been observed clinically. The patient and her parents are satisfied with the results.(ABSTRACT TRUNCATED AT 250 WORDS)     

Eruption process of the second molar

The second molar is located at the distal of the first molar, and we must be aware of its stage of development when we plan to move the first molar distally. Few researchers have investigated the development of second molars. The purpose of this study was to observe the eruption process of the maxillary and mandibular second molars by using 238 panoramic radiographs. The developmental stages of the second molar were divided into four stages: the whole crown calcified = stage 1; beginning root formation = stage 2; initial formation of the radicular bifurcation = stage 3; and the root length is equal to the crown height = stage 4. The mesiodistal crown width of the first and second molars, axial inclination and eruption rate of the second molar, and the space available for emergence of the second molar at each stage were measured, and the statistical analysis was made to assess the developmental changes. It was learned that the mandibular second molars began to erupt at stage 3 and the maxillary second molars at stage 2. The axial inclination of the mandibular second molars maintained almost the same angle and the maxillary second molars were uprighted gradually from stage 1 to 4. The available space increased significantly from stage 1 to 2 in both second molars. It is suggested that the space available for emergence of the second molar is prepared before stage 2, and then the tooth begins to erupt. As the maxillary second molars, there was further increase in the available space after stage 3. Negative correlation was seen between the mesiodistal crown width of the mandibular second molar and the available space in stage 2. Positive correlation was seen between the mesiodistal crown width of maxillary second molar and the available space in stage 3. It is suggested that greater increase in the space available for emergence of the second molar could be expected in the maxillary dental arch, if the mesiodistal crown width of the second molar required it.     

Influence of conventional and digital intraoral impressions on the fit of CAD/CAM-fabricated all-ceramic crowns

Objectives

To compare the fit of all-ceramic crowns fabricated from conventional silicone impressions with the fit of all-ceramic crowns fabricated from intraoral digital impressions.

Methods

Thirty patients with 30 posterior teeth with a prosthetic demand were selected. Zirconia-based ceramic crowns were made using an intraoral digital impression system (Ultrafast Optical Sectioning technology) (digital group, D) and 2-step silicone impression technique (conventional group, C).To replicate the interface between the crown and the preparation, each crown was cemented on its corresponding clinical preparation using ultra-flow silicone. Each crown was embedded in resin to stabilize the registered interface. Specimens were sectioned in buccolingual orientation, and internal misfit was measured at different areas using stereomicroscopy (×40).Data was analysed using Student’s t test and Mann-Whitney test (α = 0.05).

Results

No statistically significant differences were found (P > 0.05) between two groups. The mean internal misfit and mean marginal misfit were 170.9 μm (SD = 119.4)/106.6 μm (SD = 69.6) for group D and 185.4 μm (SD = 112.1)/119.9 μm (SD = 59.9) for group C.

Conclusion

Ceramic crowns fabricated using an intraoral scanner are comparable to elastomer conventional impressions in terms of their marginal and internal fits. The mean marginal fit in both groups was within the limits of clinical acceptability.

Clinical significance

Impressions based on Ultrafast Optical Sectioning technology can be used for manufacturing ceramic crowns in a normal workflow, with the same results as silicone conventional impressions.

     

A Technique to Evaluate the Space for Retentive Components under a Removable Prosthesis

Space analysis for retentive components is a critical part of a treatment plan for an implant‐retained prosthesis. This article describes a technique to evaluate the retentive component space between the mucosa and intaglio surface of a removable prosthesis. This technique uses a silicone mold to represent the relieved space. Two silicone matrices are fabricated over the silicone space replica as a reference for selecting or fabricating retentive components for the implant‐retained removable prosthesis.     

下颌骨几个变量与第三磨牙阻生的关系

目的:分析下颌骨几个变量与第三磨牙阻生的关系,以了解下颌第三磨牙阻生的发病机理.方法:曲面断层X线片83张,将146侧无缺牙、无多生牙且牙列无明显拥挤者测量下颌第三磨牙倾斜角(θ)、下颌角(a)、下颌骨嵴缘夹角(β)、磨牙后间隙长度(BX)、下颌骨牙槽长度(OB)和第三磨牙牙冠宽度(MD)并将结果进行分析.结果:磨牙后间隙长度、下颌骨牙槽长度和第三磨牙牙冠宽度与第三磨牙阻生相关,下颌角和嵴缘夹角角度与阻生牙无关.结论:下颌第三磨牙阻生与下颌骨发育相关,磨牙后间隙的长度、磨牙后间隙长度与第三磨牙牙冠宽度比值是主要的影响因素.