Heeje Lee

The accuracy of implant impressions: A systematic review

STATEMENT OF PROBLEMnVarious implant impression techniques, such as the splint, pick-up, and transfer techniques, have been introduced, and some techniques may be more accurate than others. Also, clinically, some factors, including the angulation or depth of implants, may affect the accuracy of the implant impressions.nnnPURPOSEnThe purposes of this review were to: (1) investigate the accuracy of published implant impression techniques, and (2) examine the clinical factors affecting implant impression accuracy.nnnMATERIAL AND METHODSnAn electronic search was performed in June 2008 of MEDLINE, EMBASE, and Cochrane Library databases with the key words implant, implants, impression, and impressions. To be included, the study had to investigate the accuracy of implant impressions and be published in an English peer-reviewed journal. In addition, a hand search was performed to enrich the results for the time period from January 1980 to May 2008. After executing the search strategies, 41 articles were selected to be included in the review process.nnnRESULTSnAll of the selected articles were in vitro studies. Of the 17 studies that compared the accuracy between the splint and nonsplint techniques, 7 advocated the splint technique, 3 advocated the nonsplint technique, and 7 reported no difference. Fourteen studies compared the accuracy of pick-up and transfer impression techniques, and 5 showed more accurate impression with the pick-up techniques, 2 with the transfer technique, and 7 showed no difference. The number of implants affected the comparison of the pick-up and splint techniques. Eleven studies compared the accuracy of polyether and vinyl polysiloxane (VPS), and 10 of 11 reported no difference between the 2 materials. Four studies examined the effect of implant angulation on the accuracy of impressions. Two studies reported higher accuracy with straight implants, while the other 2 reported there was no angulation effect.nnnCONCLUSIONSnThe review of abutment level or implant level internal connection implants indicated that more studies reported greater accuracy with the splint technique than with the nonsplint technique. For situations in which there were 3 or fewer implants, most studies showed no difference between the pick-up and transfer techniques, whereas for 4 or more implants, more studies showed higher accuracy with the pick-up technique. Polyether and VPS were the recommended materials for the implant impressions.

Effect of subgingival depth of implant placement on the dimensional accuracy of the implant impression: An in vitro study

STATEMENT OF PROBLEMnIn some instances, an implant needs to be placed deep subgingivally, which may result in a less accurate impression of the implant. PURPOSE.: The purpose of this study was to evaluate the effect of subgingival depth of implant placement on the accuracy of implant impressions.nnnMATERIAL AND METHODSnA stone master model was fabricated with 5 implant analogs (RN synOcta analog), embedded parallel to each other, at the center (E) and the 4 corners (A, B, C, and D). The vertical position of the shoulders of the implants was intentionally different among the implants: A and E were flush with the top surface of the model; B was 2 mm below, and C and D were 4 mm below the surface. The horizontal distances of implants A, B, C, and D from E were measured with a measuring microscope. A cross-shaped metal measuring bar was then fabricated and connected to E, with the arms of the casting designed to be 2 mm above the top surface of the model and incorporating a reference mark. With the measuring bar connected to E, the vertical distances from the apical surface of A, B, C, and D to the measuring reference marks were measured with a digital micrometer. The body of the impression coping for implant D was modified by adding 4 mm of additional impression coping, while standard impression copings were used for all other implants. Open tray impressions were made using medium-body polyether material (Impregum Penta) or a combination of putty and light-body vinyl polysiloxane (VPS) material (Elite HD+) (n=15). Then casts were poured with type IV dental stone. The vertical and horizontal distances of the casts were measured with the methods outlined above for the master model. The distortion values that were determined as differences between the measurements of the master model and those of the casts were collected for statistical analysis. Two-way and 1-way repeated measures ANOVA followed by Tukeys HSD test were performed to compare the distortion values (alpha=.05).nnnRESULTSnFor vertical measurements, 2-way repeated measures ANOVA showed no significant depth (P=.36), material (P=.24), or interaction effects (P=.06). However, it showed significant depth effect for horizontal measurements (P=.01). Within the polyether group, 1-way repeated measures ANOVA showed significant differences in horizontal measurements among the implants with different depths (P=.03). The post hoc Tukeys test showed that the impression of 4-mm-deep implants with normal impression copings (C) was significantly less accurate than impressions of 0-mm-deep implants (A) (P=.02). Within the VPS group, there was no significant difference among the implants with different depths (P=.09).nnnCONCLUSIONSnThere was no effect of implant depth on the accuracy of the VPS group. However, for the polyether group, the impression of an implant placed 4 mm subgingivally showed a greater horizontal distortion compared to an implant placed more coronally. Adding a 4-mm extension to the retentive part of the impression coping eliminated this difference.

The influence of veneering porcelain thickness of all-ceramic and metal ceramic crowns on failure resistance after cyclic loading

STATEMENT OF PROBLEMnIn some clinical situations, the length of either a prepared tooth or an implant abutment is shorter than ideal, and the thickness of a porcelain crown must be increased. Thickness of the coping and the veneering porcelain should be considered to prevent mechanical failure of the crown.nnnPURPOSEnThe purpose of this study was to investigate the influence of veneering porcelain thickness for all-ceramic and metal ceramic crowns on failure resistance after cyclic loading.nnnMATERIAL AND METHODSnAll-ceramic and metal ceramic crowns (n=20) were fabricated on an implant abutment (RN Solid Abutment) for the study. Two different framework designs with 2 different incisal thicknesses of veneering porcelain (2 mm and 4 mm) were used for each all-ceramic and metal ceramic crown system, resulting in 4 experimental groups (n=10) with identically shaped crowns. The all-ceramic crown consisted of alumina (Procera AllCeram) frameworks and veneering porcelain (Cerabien), while metal ceramic crowns were made of high noble metal (Leo) frameworks and veneering porcelain (IPS Classic). All crowns were cemented on the corresponding abutments using a resin cement (Panavia 21). They were subjected to 1000 cycles of thermal cycling (5 degrees C and 55 degrees C; 5-second dwell time). The crowns were tested with a custom-designed cyclic loading apparatus which delivered simultaneous unidirectional cyclic loading at 135 degrees, vertically, at an rpm of 250, with a load of 49 N. Each specimen was loaded for 1.2 x 106 cycles or until it failed. The specimens were thoroughly evaluated for cracks and/or bulk fracture with an optical stereomicroscope (x10) and assigned a score of success, survival, or failure. The specimens without bulk fracture after cyclic loading were loaded along the long axis of the tooth, on the incisal edge, in a universal testing machine at a crosshead speed of 1.5 mm/min, until fracture. Fishers exact test was used to compare the success and survival rate between the 2 different materials (alpha=.05). Two-way ANOVA was used to analyze data in terms of material, porcelain thickness, and interaction effect. Also, a 2-sample t test was performed to compare between 2 thicknesses within the same material (alpha=.05).nnnRESULTSnAccording to the Fishers exact test, the all-ceramic group showed significantly higher success (P=.003) and survival rates (P=.001) than the metal ceramic group. For the failure load, the 2-way ANOVA showed significant effects for material (P<.001) and porcelain thickness (P=.004), but not a significant interaction effect (P=.198). For the metal ceramic groups, crowns with a 2-mm porcelain thickness showed a significantly greater failure load than crowns with a 4-mm porcelain thickness (P=.004). However, all-ceramic groups did not show a significant difference between the 2 different thicknesses of veneering porcelain (P=.198).nnnCONCLUSIONSnThe all-ceramic crowns showed significantly higher success and survival rates after cyclic loading, but lower failure loads than metal ceramic crowns. The thickness of the veneering porcelain affected the failure load of the metal ceramic crowns, but not that of the all-ceramic crowns.

Prospective observation of CAD/CAM titanium ceramic single crowns: A three-year follow up

STATEMENT OF PROBLEMnComputer-aided design/computer-aided manufacturing (CAD/CAM) titanium ceramic restorations were developed with the potential for replacing expensive, high noble metal ceramic restorations. However, there is a lack of information about the clinical performance of CAD/CAM titanium ceramic single crowns.nnnPURPOSEnThe purpose of this study was to evaluate CAD/CAM titanium ceramic single crowns after 3 years in function.nnnMATERIAL AND METHODSnA total of 41 crowns were fabricated for 21 patients. The titanium copings were CAD/CAM milled (Everest CAD/CAM system) with an even thickness of 0.5 mm, and low-fusing veneering porcelain (Vita Titanium Porcelain) was added incrementally. The crowns were cemented using zinc phosphate cement after confirming that there were no mechanical and biological complications. The patients were recalled at 12, 24, and 36 months after cementation to examine the presence of any complications and measure periodontal parameters such as probing depth (PD), bleeding on probing (BOP), and plaque index (PI). The success and survival rates were estimated using the Kaplan-Meier analysis.nnnRESULTSnThe success rate of CAD/CAM titanium ceramic crowns with regard to mechanical complications was 82.3% (95% confidence interval: 71.2% to 95.1%). The cumulative survival rate of the crowns was 94.9% (95% confidence interval: 88.3% to 100%) after 3 years. No biological complications were observed. At the end of the follow up, PD was 2.93 mm, percentile of surface with BOP was 29.2, and PI was 0.31.nnnCONCLUSIONSnThe clinical performances of the CAD/CAM titanium ceramic crowns for 3 years were acceptable, with no biologic complications and a high cumulative survival rate.

The Influence of Verification Jig on Framework Fit for Nonsegmented Fixed Implant-Supported Complete Denture

PURPOSEnThe purpose of this retrospective study was to assess if there was a difference in the likelihood of achieving passive fit when an implant-supported full-arch prosthesis framework is fabricated with or without the aid of a verification jig.nnnMATERIALS AND METHODSnThis investigation was approved by the University of Rochester Research Subject Review Board (protocol #RSRB00038482). Thirty edentulous patients, 49 to 73 years old (mean 61 years old), rehabilitated with a nonsegmented fixed implant-supported complete denture were included in the study. During the restorative process, final impressions were made using the pickup impression technique and elastomeric impression materials. For 16 patients, a verification jig was made (group J), while for the remaining 14 patients, a verification jig was not used (group NJ) and the framework was fabricated directly on the master cast. During the framework try-in appointment, the fit was assessed by clinical (Sheffield test) and radiographic inspection and recorded as passive or nonpassive.nnnRESULTSnWhen a verification jig was used (group J, n = 16), all frameworks exhibited clinically passive fit, while when a verification jig was not used (group NJ, n = 14), only two frameworks fit. This difference was statistically significant (p < .001).nnnCONCLUSIONSnWithin the limitations of this retrospective study, the fabrication of a verification jig ensured clinically passive fit of metal frameworks in nonsegmented fixed implant-supported complete denture.

Fracture resistance of composite resin restorations and porcelain veneers in relation to residual tooth structure in fractured incisors

The aim of the present study was to investigate whether there is a direct correlation between the amount of residual tooth structure in a fractured maxillary incisor and the fracture resistance of composite resin restorations or porcelain veneers after cyclic loading. Sixty human-extracted maxillary central and lateral incisors were mounted in an acrylic block with the coronal aspect of the tooth protruding from the block surface. The teeth were assigned to two groups: 2-mm incisal fracture and 4-mm incisal fracture. Then, the teeth were further divided into two different restoration subgroups, porcelain laminate veneer and composite resin restoration, therefore obtaining four groups for the study (n=15). The specimens were subjected to 1000 cycles of thermocycling and were mechanically tested with a custom-designed cyclic loading apparatus for 2×106 cycles or until they failed. The specimens that survived the cyclic loading were loaded on the incisal edge along the long axis of the tooth with a flat stainless steel applicator until they fractured using a universal testing machine to measure the failure load. Two-way anova was used to assess the significance of restoration, amount of fracture, and interaction effect (α=0.05). During the cyclic loading, for the composite resin group, two specimens with 2-mm fracture and three specimens with 4-mm fracture failed. For the porcelain veneer group, two specimens with 2-mm fracture and one specimen with 4-mm fracture failed. The 2-way anova did not show statistical significance for restoration (P=0.584), amount of fracture (P=0.357), or interaction effect (P=0.212). A composite resin restoration and a porcelain veneer could perform similarly for replacing a fractured incisor edge up to 4mm. Other factors such as esthetic and/or cost would be considerations to indicate one treatment over the other.

The influence of incisal veneering porcelain thickness of two metal ceramic crown systems on failure resistance after cyclic loading

STATEMENT OF PROBLEMnIn some clinical situations, the length of either a prepared tooth or an implant abutment is shorter than ideal, and the occlusal clearance to be restored by a porcelain crown is large. Incisal thickness of the coping and the veneering porcelain should be considered to prevent mechanical failure of the crown.nnnPURPOSEnThe purpose of this study was to investigate the influence of incisal veneering porcelain thickness of metal ceramic systems on failure resistance after cyclic loading.nnnMATERIAL AND METHODSnWith a standardized technique, 60 metal ceramic anterior crowns with 2 different incisal thicknesses of porcelain veneer (2.0 and 4.0 mm) and 2 different metal alloys (Pisces Plus (B), base metal, and Leo (N), high noble metal) were fabricated to fit a custom abutment and divided into 4 groups (B20, B40, N20, N40) (n=15). The crowns were then cemented using resin cement (PANAVIA 21) and thermal cycled and mechanically cycle loaded (49-N load) for 2,000,000 cycles. The specimens were evaluated for cracks and/or bulk fracture with an optical stereomicroscope (x10) and assigned a score of success, survival, or failure. The specimens without bulk fracture after cyclic loading were loaded along the long axis of the tooth, on the incisal edge, in a universal testing machine at a crosshead speed of 1.5 mm/min until fracture. The fracture strength value (N) was recorded. The exact logistic regression and Fishers exact test were used to study the effect of different alloys and porcelain incisal thicknesses on the success and survival rates after cycle loading. The forces at failure (fracture) of different groups were compared using the rank transform-based nonparametric 2-way ANOVA (alpha=.05).nnnRESULTSnAccording to exact logistic regression, crowns of the high noble alloy group showed significantly higher success rates (P=.002) than those of the base metal group after cyclic loading. The success rate of the crowns with 2 mm of incisal veneering porcelain was significantly higher (P<.001) than that of the crowns with 4 mm of incisal veneering porcelain. For crowns with a 4-mm incisal thickness, N40 showed a significantly higher success rate than B40 (P=.04, Fishers exact test). As for survival rate, the exact logistic regression indicated that neither metal type (P=.11) nor thickness (P=.60) had a significant effect. The 2-way ANOVA showed a significant effect of thickness (P=.001) and no significant effect of metal type (P=.08) on the failure load.nnnCONCLUSIONSnThe high noble metal ceramic crowns demonstrated a significantly higher success rate after cyclic loading than the base metal ceramic crowns. Crowns with a porcelain incisal thickness of 2 mm showed, for both metal ceramic systems, a greater success rate than those with a 4-mm incisal thickness.

Oral rehabilitation of a 12-year-old patient diagnosed with a central giant cell granuloma using a fibula graft and an implant-supported prosthesis: A clinical report

This clinical report describes the oral rehabilitation of a 12-year-old boy with a central giant cell granuloma of the mandible. He underwent en bloc resection of a central giant cell granuloma, free vascularized fibula reconstruction, implant placement, and prosthesis fabrication. The multidisciplinary approach successfully restored function and esthetics. Considerations regarding the extensive surgical and prosthetic rehabilitation of a young adult with remaining growth are discussed.

A wax guide to measure the amount of occlusal reduction during tooth preparation in fixed prosthodontics

aAssistant Professor, Department of Prosthodontics. bAssistant Professor, Department of Prosthodontics. (J Prosthet Dent 2010;103:256-257) When preparing teeth for fixed restorations, it is crucial to have the proper amount of occlusal reduction to ensure the long-term success of restorations. Insufficient occlusal reduction of a tooth may result in failure due to lack of adequate thickness of the restoration.1 Excessive tooth reduction may compromise the retention of the restoration or vitality of the pulp.2 To aid the assessment of occlusal reduction, several techniques have been described. A piece of folded blotting paper3 or color-coded flexible clearance tabs with premeasured thickness have been placed on the prepared tooth while in the occluded position. The proper amount of reduction is verified by pulling the tab through the teeth. However, the result could be interpreted incorrectly if the patient does not occlude completely. Also, the flexible clearance tab may not show the specific area of insufficient reduction. Another reported technique involves the use of a periodontal probe placed directly over occluded soft ribbon wax on the prepared tooth.4 This method may be challenging for posterior areas with limited access and/ or visibility. Another method uses a caliper to measure the thickness of the occluded wax record.5 The use of a caliper in untrained hands could potentially introduce inaccuracy or even distortion of the wax record. A recent publication6 described combining baseplate wax of premeasured thickness with an articulating paper on the prepared surface to mark the underreduced area. However, this method provides limited information as to the actual amount of reduction. The previously mentioned methods all present some limitations in terms of accuracy, accessibility, or complexity. Therefore, a simple method is described in the present article for easily determining the amount of occlusal reduction in specific areas using a custom-made wax guide. PROCEDURE

A method to make a preliminary impression of mobile teeth.

aAssistant Professor, Department of Prosthodontics, Louisiana State University Health Sciences Center School of Dentistry. bAssistant Professor, Department of Prosthodontics, The University of Texas Health Science Center at Houston Dental Branch. (J Prosthet Dent 2009;102:52-53) Various techniques of making an impression for an immediate denture have been reported to prevent periodontally compromised teeth with increased mobility from being accidentally exfoliated during the impression procedure.1-4 The techniques include using plaster1 or vinyl polysiloxane putty2 for the anterior labial segment, covering the mobile teeth with copper bands,3 or making a second impression using irreversible hydrocolloid for the teeth portion over an impression of the tissue made previously with an open tray.4 Even before making the definitive impression, prevention of unexpected tooth removal during the preliminary impression phase is a challenge when treating patients who present with extremely mobile teeth. A technique of blocking out the undercut using wax has been commonly used,5 but evenly placing wax could be uncomfortable to the patient, or the anatomic structures around the teeth may not be impressed accurately due to excessive block out. Furthermore, if multiple teeth are retained with different long axes, separating the impression could dislodge some of the teeth for which the long axes are inconsistent with the path of removal. This article describes a simple and safe method to make a preliminary impression in the situation of a patient with extremely mobile teeth. The impression is made using a combination of irreversible hydrocolloid and vinyl polysiloxane interocclusal record material, without any block-out material. The materials set rapidly intraorally, and the impression is separated in 2 different directions so as not to irritate the mobile teeth. PROCEDURE