A clinical study comparing marginal and occlusal accuracy of crowns fabricated from double-arch and complete-arch impressions

BACKGROUND: The double-arch impression technique is widely used in the provision of laboratory fabricated restorations. However, there is little clinical evidence to support or refute its use. The aim of this prospective clinical study was to evaluate the occlusion and marginal fit of posterior full crowns made from double-arch impressions, and to compare these to control crowns fabricated from conventional complete-arch impressions. METHODS: Ten patients requiring single posterior ceramo-metal full crowns had both double-arch and complete-arch impressions taken of the prepared tooth. Two crowns were fabricated for each tooth, using the casts made from both impression methods. Both crowns were tried in and the occlusion and margins evaluated. The results were composed using nonparametric statistical analysis with the probability level for significance at alpha=0.05. RESULTS: The crowns fabricated from the double-arch impression were found to be more accurate in closure to the intercuspal position and had fewer interferences in lateral excursions. There were no significant differences between the two crown groups regarding protrusive interferences and margin quality. CONCLUSIONS: Crowns fabricated from the double-arch impressions were equivalent in marginal accuracy and superior occlusally to crowns fabricated from the complete-arch impressions.     

A clinical pilot study of the dimensional accuracy of double-arch and complete-arch impressions

STATEMENT OF PROBLEM: It has been suggested that articulated casts fabricated with the double-arch impression technique may have superior occlusal accuracy than those fabricated with a single complete-arch impression. However, lack of tray rigidity may lead to flexure of the impression/tray complex, resulting in inaccurate dies in the bucco-lingual dimension. PURPOSE: This clinical pilot study compared the dimensions of dies fabricated with 3 types of double-arch impressions to dies fabricated with the conventional complete-arch, custom tray method. MATERIAL AND METHODS: Thirty-five addition silicone impressions were made of cast metal copings cemented onto natural teeth prepared as complete-crown abutments. Four combinations of tray types and impression material viscosity were used: (1) complete-arch, custom acrylic trays loaded with heavy-bodied material; (2) double-arch, disposable plastic trays loaded with heavy-bodied material; (3) double-arch, disposable plastic trays loaded with putty material; and (4) double-arch, reusable brass metal trays loaded with heavy-bodied material. Immediately prior to tray insertion, light-bodied impression material was syringed over all copings as a wash. The 4 copings were fabricated from cast gold and simulated metal-ceramic complete-crown thimbles with polished collars and had "projections" on the occlusal surfaces. The impressions were poured in type IV die-stone. Bucco-lingual and inter-abutment dimensions were measured. The differences between the stone dimensions and cast metal control dimensions were calculated and converted to percent dimensional change. The data were analyzed with 1-way analysis of variance, Student t tests, and Mann-Whitney tests (P<.05). RESULTS: The plastic double-arch tray loaded with heavy-viscosity addition silicone and a low-viscosity wash produced the least accurate combination inter- and intra-abutment dimensions. For this protocol, 1.17% mean dimensional change was recorded. This result was significantly different than that obtained for the other 3 impression methods tested. No significant differences were found between the complete-arch method and protocols in which putty was loaded in a plastic or metal tray. CONCLUSION: Within the limitations of this pilot study, the more rigid tray/impression material combinations more accurately replicated stone dies.     

Determining the accuracy of stock and custom tray impression/casts

SUMMARY A study was conducted to evaluate the accuracy of casts made from stock tray and custom tray impressions using polysiloxane impression material. The results indicate that all casts distort but that impressions made from custom trays were more accurate and consistent in reproduction than were stock tray impressions.     

The effect of tray selection,viscosity of impression material,and sequence of pour on the accuracy of dies made from dual-arch impressions

STATEMENT OF PROBLEM: Dual-arch trays are often used to generate impressions of prepared teeth and of the opposing arch simultaneously. There is concern that accuracy of the casts generated with this technique can be affected by the type of tray, viscosity of the impression material, and sequence of pouring the cast. PURPOSE: This study compared the accuracy of working dies made from impressions with metal and plastic dual-arch trays, for 2 different viscosities of impression tray material and by altering which side of the impression was poured first. MATERIALS AND METHODS: Impressions were made of a typodont mandibular arch containing a circular stainless steel crown preparation (standard). There were 3 variables: type of dual-arch tray, impression material viscosity, and order of pour of the impressioned arches. A balanced design with independent samples was used (n=10). Two types of dual-arch trays, plastic (Triple Tray) and metal (COE Impression Tray), and 2 viscosities of addition silicone for the tray were used (Aquasil Rigid and Aquasil Monophase). Type IV gypsum (Fuji-Rock) with a ratio of 20 mL of distilled water to 100 g of powder was hand-mixed for 10 seconds then mixed under vacuum for 40 seconds and poured into the trays while being vibrated. One side of the dual-arch impression was poured with 35 g of stone and allowed to set for 1 hour before the other side was poured with 35 g of stone. The order of pour was randomized, and all casts were allowed to set for 24 hours at room temperature before removal. The dies were measured in 3 dimensions (buccolingual, mesiodistal, and occlusogingival) with a measuring microscope. The gypsum working dies were placed into a custom jig fabricated to permit measurement at a fixed, reproducible position under the microscope. Each dimension of the working dies was measured 3 times, and the mean was used for the sample value. The same 3 aspects of the stainless steel standard were measured multiple times, before and then at the conclusion of measuring all working dies, to arrive at the 3 standard values to which all working die means were compared. The means for the standard used in the statistical analysis were those taken at the conclusion of the study. The intraexaminer variation for measuring the standard was 0.001 mm. A 3-factor analysis of variance was used for the statistical analysis with hypothesis testing at alpha=.05. RESULTS: Statistically significant differences were found with viscosity selection for the buccolingual and occlusogingival dimensions of the working die. The rigid material produced working dies slightly taller (1 microm) than the standard, and those from the monophase material were 4 microm shorter. Regarding tray selection, metal trays were slightly more accurate in the mesiodistal dimension, and when monophase was used in a plastic tray, gypsum dies were nearly 30 microm smaller in the mesiodistal dimension (P<.05). Differences were not detected for sequence of pouring impressions. CONCLUSION: Within the limitations of this study, the monophase material, when compared with the rigid impression material, was most accurate for the occlusogingival and mesiodistal dimensions, although not as accurate in the buccolingual. This buccolingual difference (0.002 mm-0.006 mm) would be clinically inconsequential with the application of die spacer. The rigid impression material was also unaffected by tray selection for the mesiodistal, whereas monophase was affected. When a monophase impression material was used, plastic dual-arch trays yielded gypsum dies which were significantly smaller (0.029 mm) than the ones generated from the metal trays (0.006 mm). Thus rigid impression materials can be recommended for use in dual-arch trays; however, the magnitude of the differences would generally not be clinically significant because they could be compensated for with several coats of die spacer.     

A quadrant tray and bite registration as an alternative to dual-arch impressions for fixed prosthetics: a clinical and dental laboratory technique

To perform fixed prosthodontic procedures, dentists take a full-arch or quadrant impression and articulate the casts. The dual-arch impression technique is a popular quadrant technique for crown fabrication. The technique described in this article, which uses a quadrant impression and separate interocclusal record, offers several advantages over the traditional dual-arch method.     

Transfer accuracy of 3D-printed trays for indirect bonding of orthodontic brackets:: A clinical study

ObjectivesTo evaluate the transfer accuracy of 3D-printed indirect bonding trays constructed using a fully digital workflow in vivo.Materials and MethodsTwenty-three consecutive patients had their incisors, canines, and premolars bonded using fully digitally designed and 3D-printed transfer trays. Intraoral scans were taken to capture final bracket positioning on teeth after bonding. Digital models of postbonding scans were superimposed on those of corresponding virtual bracket setups, and bracket positioning differences were quantified. A total of 363 brackets were evaluated. One-tailed t-tests were used to determine whether bracket positioning differences were within the limit of 0.5 mm in mesiodistal, buccolingual, and occlusogingival dimensions, and within 2° for torque, tip, and rotation.ResultsMean bracket positioning differences were 0.10 mm, 0.10 mm, and 0.18 mm for mesiodistal, buccolingual, and occlusogingival measurements, respectively, with frequencies of bracket positioning within the 0.5-mm limit ranging from 96.4% to 100%. Mean differences were significantly within the acceptable limit for all linear dimensions. Mean differences were 2.55°, 2.01°, and 2.47° for torque, tip, and rotation, respectively, with frequencies within the 2°-limit ranging from 46.0% to 57.0%. Mean differences for all angular dimensions were outside the acceptable limit; however, this may have been due to limitations of scan data.ConclusionsIndirect bonding using 3D-printed trays transfers planned bracket position from the digital setup to the patient''s dentition with a high positional accuracy in mesiodistal, buccolingual, and occlusogingival dimensions. Questions remain regarding the transfer accuracy for torque, tip, and rotation.     

A laboratory study of dimensional changes for three elastomeric impression materials using custom and stock trays

Clinical success of fixed prosthodontic procedures is dependent in part upon the dimensional accuracy of elastomeric impression materials and impression procedures. Three elastomeric impression materials were used in custom and stock trays to determine the accuracy of impressions taken from an experimental stainless steel model representing premolar and molar bridge abutment preparations. Horizontal and vertical individual abutment and interabutment dimensions were measured on die stone replicas, and the measurements compared with those obtained from stainless steel master models. The results of this study demonstrate polysulphide is the least accurate impression material for both vertical and horizontal individual abutment dimensions. However, for interabutment horizontal dimensions, no statistical differences were noted between impression material types when using a custom tray. Stock trays produced unreliable results for all the materials tested.     

A practice-based assessment of the handling of a fast-setting polyvinyl siloxane impression material used with the dual-arch tray technique.

OBJECTIVE: The purpose of this study was to assess a new impression material used in conjunction with the dual-arch technique. METHOD AND MATERIALS: Ten members were selected at random from the Product Research and Evaluation by Practitioners (PREP) panel, a United Kingdom-based group of dental practitioners who are prepared to undertake research projects in their practices. Explanatory letters, a questionnaire, packs of the impression material, and dual-arch trays were distributed to the evaluators, together with instructions on the use of the materials. The practitioners were asked to use the materials and return the questionnaire after using the materials for a minimum of 10 impressions. RESULTS: Three evaluators had not previously used the dual-arch technique, six had used it in the past or occasionally, and one used the technique routinely. A total of 115 impressions were recorded with Quick Step. The overall rating for ease of removal of impressions from the mouth was 4.7 on a linear scale in which 5 represented easy to remove and 1 represented difficult to remove. Four of the evaluators rated the working time as excellent and the remaining six as good. Eight of the evaluators stated that the quality of fit of the single-unit restoration constructed with the combined-arch tray was the same as that obtained when a conventional tray technique was used. CONCLUSIONS: The impression material under test scored highly for application in circumstances where the fields above and below the preparation margin were dry or had limited moisture problems. Eighty percent of the evaluators considered the impression and dual-arch tray technique to be of benefit to their practice.     

A randomized clinical trial comparing the accuracy of direct versus indirect bracket placement

OBJECTIVE: To determine the accuracy of direct or indirect bracket placement. DESIGN: A prospective, randomized comparison of 2 different methods of bracket placement. SETTING: Queens Hospital, Burton upon Trent, UK between February and May 2001.Materials and method: Twenty-six consecutive patients requiring upper and lower MBT trade mark pre-adjusted Edgewise appliances had their labial segments bonded directly or indirectly according to a split mouth system of allocation. Before and after bond-up all brackets were photographed and measured from tracings to determine positional differences from the ideal. RESULTS: Using ANOVA (General Linear Model), vertical errors were found to be greater than those in the horizontal plane, which in turn were greater than angular errors (p<0.05). Errors were greater in the maxillary arch than in the mandibular arch. There was no significant difference between the mean errors produced by the two methods of bracket placement. CONCLUSIONS: Mean bracket placement errors were similar with both techniques.     

A randomized clinical trial comparing the accuracy of direct versus indirect bracket placement

Abstract

Objective: To determine the accuracy of direct or indirect bracket placement.

Design: A prospective, randomized comparison of 2 different methods of bracket placement.

Setting: Queens Hospital, Burton upon Trent, UK between February and May 2001.

Materials and method: Twenty-six consecutive patients requiring upper and lower MBT? pre-adjusted Edgewise appliances had their labial segments bonded directly or indirectly according to a split mouth system of allocation. Before and after bond-up all brackets were photographed and measured from tracings to determine positional differences from the ideal.

Results: Using ANOVA (General Linear Model), vertical errors were found to be greater than those in the horizontal plane, which in turn were greater than angular errors (p<0.05). Errors were greater in the maxillary arch than in the mandibular arch. There was no significant difference between the mean errors produced by the two methods of bracket placement.

Conclusions: Mean bracket placement errors were similar with both techniques.     

A clinical study to evaluate the efficacy of a novel tray based tooth whitening system

OBJECTIVES: The study was designed to test the whitening efficacy of a new prefabricated tray based whitening system. METHODS: A parallel, examiner blind, stratified two group clinical study was carried out in the Department of Fixed and Removable Prosthodontics, Leeds Dental Institute, United Kingdom. Forty-nine male and female subjects aged 18-70 years participated in the study and they underwent both clinical and digital evaluation at baseline, 3, 7 and 14 days, respectively. The non-intervention control group was given no treatment and the test group received a tray based whitening system (Colgate Visible White PF Mint, Colgate Palmolive Company, NY, USA) that uses a 6% hydrogen peroxide gel applied in the tray twice daily for 30 min. Digital images of teeth were captured using a Jai 3CCD digital camera under an annular LED illumination array (SCHOTT North America, Inc., USA) and the data obtained was used to calculate colour parameters (L(*), a(*) and b(*)) and whiteness index WIO. RESULTS: Clinical data and digital data showed significant difference for the Visible White group from the control group for the mean difference in its values from the baseline to each visit (p<0.001). Digital data showed significant correlation to clinical data. CONCLUSION: In the present study statistically significant tooth whitening was evident after 3 days treatment with the tray based whitening system and colour improved with continued usage over 14 days. It also supports our previous study results that the WIO index is appropriate for assessing changes in tooth whiteness.     

Impact of scanning strategy on the accuracy of complete-arch intraoral scans: a preliminary study on segmental scans and merge methods

PURPOSEThis study investigated the accuracy of full-arch intraoral scans obtained by various scan strategies with the segmental scan and merge methods.MATERIALS AND METHODSSeventy intraoral scans (seven scans per group) were performed using 10 scan strategies that differed in the segmental scan (1, 2, or 3 segments) and the scanning motion (straight, zigzag, or combined). The three-dimensional (3D) geometric accuracy of scan images was evaluated by comparison with a reference image in an image analysis software program, in terms of the arch shape discrepancies. Measurement parameters were the intermolar distance, interpremolar distance, anteroposterior distance, and global surface deviation. One-way analysis of variance and Tukey honestly significance difference post hoc tests were carried out to compare differences among the scan strategy groups (α = .05).RESULTSThe linear discrepancy values of intraoral scans were not different among scan strategies performed with the single scan and segmental scan methods. In general, differences in the scan motion did not show different accuracies, except for the intermolar distance measured under the scan conditions of a 3-segmental scan and zigzag motion. The global surface deviations were not different among all scan strategies.CONCLUSIONThe segmental scan and merge methods using two scan parts appear to be reliable as an alternative to the single scan method for full-arch intraoral scans. When three segmental scans are involved, the accuracy of complete arch scan can be negatively affected.     

A two-year clinical trial comparing the retention of two fissure sealants.

A clinical evaluation of an experimental resin sealant (ICI 209085) was made by comparing it with a previously investigated and well recognized material (Light Cured Tinted Delton). The two materials were bilaterally placed in 117 pairs of teeth (48 premolars and 69 molars) in 60 children aged 6-14 years. The children were re-examined after 6, 12 and 24 months. The overall rates of full retention were 97.4% in teeth sealed with the experimental sealant and 96.6% in those sealed with the control sealant, while the corresponding figures for partial retention were 2.6% and 3.4%. From none of the teeth were the sealants totally lost. No carious lesions developed in the sealed fissures during the trial. It is concluded that the experimental sealant is comparable with the control sealant with respect to retention and caries prevention.     

前方牵引矫治器不同力值反作用力的三维有限元分析

目的：通过建立包含颞下颌关节的颅颌面三维有限元模型,模拟前方牵引矫治器反作用力的加力方式,分析其在颞下颌关节区、颌骨的应力分布情况以及对各部位节点位移的影响。方法：选择1名健康男性受试者,通过CT扫描得到颅颌面的二维图像数据,借助Mimics、Magics、MSC等专用软件,采用连续、均质、线性、各向同性的线弹性材料,建立包括颞下颌关节和上、下颌骨的颅颌面三维有限元模型。然后在此基础上,根据前方牵引装置的反作用力原理建立加力模型,即采用与平面成后上方37°的施力方向,于下颌最底部加载3~6 N的力值,采用ANSYS10.0有限元分析软件,测定颞下颌关节区、颌骨的应力分布情况以及各部分位移的变化,并对结果进行分析、归纳和整理。结果：在同一角度下,关节窝和髁突头、颈部应力随加载力的增大而增大,下颌最大应力出现在节点力加载部位颏部,上颌最大应力出现在刚性固定面。同时该模型出现微小的位移变化,颅颌面各部分位移随节点力的增大而增大,颅上颌位移由颅底部和平面向颅顶部逐渐减小,下颌骨的位移由前部到后部逐渐减小,并出现顺时针方向旋转。结论：前方牵引矫治器对颞下颌关节区及颌骨产生反作用力的影响,且随着加载力的增大,其产生的反作用力和形变随之增大。颏部可能出现变形,下颌顺时针方向旋转。     

Evaluation of the trueness and precision of eight extraoral laboratory scanners with a complete-arch model: a three-dimensional analysis

PurposeThe purpose of this study was to evaluate the trueness and precision of eight different extraoral laboratory scanners using three-dimensional (3D) analysis method.MethodAn arch-shaped master model was designed with a computer software (Rapidform XOR2) and manufactured with a 3D printer (Projet 3510 MP). Then the master model was digitized with an industrial 3D scanner (ATOS Core 200). With each scanner master model was scanned ten times and stereolithography (.stl) data were imported into 3D analysis software (Geomagic Control). Accuracy was determined with evaluating trueness and precision.ResultsTrueness of the scanners were 27.5 μm for 7 series; 30.9 μm for D640; 26.8 μm for D710; 33.3 μm for Activity 102; 32.4 μm for Tizian Smart-Scan; 21.6 μm for NeWay; 26.1 μm for inEOS X5 and 17,47 μm for D2000. 28.2 μm for laser; 32.9 μm for white light and 21.7 μm for blue light scanners. Significant differences were found between scanners (p < .001), (p < .001). Precision of the scanners were 30.1 μm for 7 series; 31.7 μm for D640; 26.3 μm for D710; 22.7 μm for Activity 102; 25.1 μm for Tizian Smart-Scan; 15.7 μm for NeWay; 26.1 μm for inEOS X5; 16.6 μm for D2000. 29.2 μm for laser; 24.4 μm for white light and 19.2 μm for blue light scanners. Significant differences were found between scanners (p < .001), (p = .027).ConclusionsThe systems that had the best combination of trueness and precision for complete-arch scanning were D2000 and NeWay. Scanners using blue-light showed more accurate results than the white-light and laser scanners.     

Accuracy of complete dental arch impressions and stone casts using a three-dimensional measurement system. Effects on accuracy of rubber impression materials and trays

The purpose of this study was to investigate and compare the accuracy of complete dental arch impressions and stone casts made with two kinds of impression materials (addition-type silicone and polysulfide rubber) and trays (custom tray and modified custom tray). In addition, the effect of the quantity of stone was examined. Impressions were made from a metallic model of a simplified maxillary dentition. Impressions and stone casts were measured respectively with a three-dimensional measuring microscope. The results were as follows: 1. Distortions of impressions were so small that the reproducibilities of impressions were superior three-dimensionally. These kinds of impressions and trays did not influence the accuracy of impressions. 2. The setting expansion of the stone in the impression occurred in the outward direction and was affected by the kinds of impressions and trays. 3. The arch widths and lengths of the stone casts tended to increase in number. 4. Stone casts made with addition-type silicone impression material and a custom tray were the most accurate because the combination of the impression material and tray effectively suppressed the setting expansion of stone. 5. The accuracy of stone casts could be improved by controlling the quantity of stone.     

A clinical study comparing the efficacy and sensitivity of home vs combined whitening

This randomized clinical study assessed efficacy in terms of color change and production of sensitivity after home whitening alone and home whitening supplemented with in-office bleaching. Thirty-six subjects (aged 19 to 58 years) were randomly assigned to one of three different treatment groups: (A) home whitening for two weeks, with 16% carbamide peroxide in custom-made trays; (B) home whitening for two weeks, with 16% carbamide peroxide in custom-made trays supplemented with in-office bleaching with 9% hydrogen peroxide (in the same trays); or (C) home whitening for two weeks, with 16% carbamide peroxide in custom-made trays supplemented with in-office bleaching with 27% hydrogen peroxide (in the same trays). The efficacy of tooth whitening was assessed by determining the color change associated with the six upper anterior teeth using a value-ordered shade guide. Sensitivity was self-assessed with the use of a visual analog scale (VAS). Tooth shade and sensitivity were assessed at the following points: pretreatment; immediately after the home whitening phase; immediately after the in-office phase (groups B and C); and one week post active treatment. At the one week follow-up visit, subjects in group A had a mean (SD) color change of 5.9 (1.83) (teeth were lighter) immediately after cessation of treatment (p<0.01). Subjects in groups B and C experienced a greater change in mean (SD) shade immediately following their respective in-office treatments of 5.1 (1.53) and 5.4 (1.55). However, within one week, the shade of these teeth regressed to a similar degree to that achieved by subjects treated in group A. Overall, no significant difference in shade change or sensitivity was produced between the three groups. Investigators concluded that the in-office element of combined whitening produced no significant difference in tooth color or sensitivity when compared with home whitening alone.