Sang J. Lee

Accuracy of digital versus conventional implant impressions

OBJECTIVE The accuracy of digital impressions greatly influences their clinical viability in implant restorations. The aim of this study was to compare the accuracy of gypsum models acquired from the conventional implant impression to digitally milled models created from direct digitalization by three-dimensional analysis. MATERIALS AND METHODS Thirty gypsum and 30 digitally milled models, impressed directly from a reference model, were prepared. The models and reference model were scanned by a laboratory scanner, and 30 surface tessellation language datasets from each group were imported to an inspection software program. The datasets were aligned to the reference dataset by a repeated best-fit algorithm, and 10 specified contact locations of interest were measured in mean volumetric deviations. The areas were pooled by cusps, fossae, interproximal contacts, horizontal and vertical axes of implant position and angulation. The pooled areas were statistically analysed by comparing each group to the reference model to investigate the mean volumetric deviations accounting for accuracy and standard deviations for precision. RESULTS Milled models from digital impressions had comparable accuracy to gypsum models from conventional impressions. However, differences in fossae and vertical displacement of the implant position from the gypsum and digitally milled models compared to the reference model exhibited statistical significance (P < 0.001, P = 0.020, respectively). CONCLUSION Milled models from digital impression are comparable to gypsum models from conventional impression.

An evaluation of student and clinician perception of digital and conventional implant impressions.

STATEMENT OF PROBLEM The accuracy and efficiency of digital implant impressions should match conventional impressions. Comparisons should be made with clinically relevant data. PURPOSE The purpose of this study was to evaluate the difficulty level and operators perception between dental students and experienced clinicians when making digital and conventional implant impressions. MATERIAL AND METHODS Thirty experienced dental professionals and 30 second-year dental students made conventional and digital impressions of a single implant model. A visual analog scale (VAS) and multiple-choice questionnaires were used to assess the participants perception of difficulty, preference, and effectiveness. Wilcoxon signed-rank test within the groups and Wilcoxon rank-sum test between the groups were used for statistical analysis (α=.05). RESULTS On a 0 to 100 VAS, the student group scored a mean difficulty level of 43.1 (±18.5) for the conventional impression technique and 30.6 (±17.6) for the digital impression technique (P=.006). The clinician group scored a mean (standard deviation) difficulty level of 30.9 (±19.6) for conventional impressions and 36.5 (±20.6) for digital impressions (P=.280). Comparison between groups showed a mean difficulty level with the conventional impression technique significantly higher in the student group (P=.030). The digital impression was not significantly different between the groups (P=.228). Sixty percent of the students preferred the digital impression and 7% the conventional impression; 33% expressed no preference. In the clinician group, 33% preferred the digital impression and 37% the conventional impression; 30% had no preference. Seventy-seven percent of the student group felt most effective with digital impressions, 10% with conventional impressions, and 13% with either technique, whereas 40% of the clinician group chose the digital impression as the most effective technique, 53% the conventional impression, and 7% either technique. CONCLUSIONS The conventional impression was more difficult to perform for the student group than the clinician group; however, the difficulty level of the digital impression was the same in both groups. It was also determined that the student group preferred the digital impression as the most efficient impression technique, and the clinician group had an even distribution in the choice of preferred and efficient impression techniques.

Bond strength of the porcelain repair system to all-ceramic copings and porcelain.

PURPOSE The purpose of this study was to investigate the shear bond strength of the porcelain repair system on alumina and zirconia core ceramics, comparing this strength with that of veneering porcelain. MATERIALS AND METHODS Veneering ceramic (n = 12), alumina core (n = 24), and zirconia core (n = 24) blocks measuring 10 × 5 × 5 mm(3) were fabricated. Veneering ceramic blocks were used as the control. Alumina and zirconia core blocks were divided into 2 groups (n = 12 each), and a slot (2 × 2 × 4 mm(3)) filled with veneering ceramics was prepared into one of the alumina and zirconia core groups (n = 12). Followed by surface treatments of micro-abrasion with 30 μm alumina particles, etching with 35% phosphoric acid and silane primer and bond, composite resin blocks (2 × 2 × 2 mm(3)) were built up and light polymerized onto the treated surfaces by 3 configurations: (a) composite blocks bonded onto veneering ceramic surface alone, (b) composite blocks bonded onto alumina core or zirconia core surfaces, (c) a 50% surface area of the composite blocks bonded to veneering ceramics and the other 50% surface area of the composite blocks to alumina core or zirconia core surfaces. The shear bond strength of the composite to each specimen was tested by a universal testing machine at a 0.5 mm/min crosshead speed. The shear bond strength was analyzed by unpaired t-tests for within the configuration groups and ANOVA for among the different configuration groups. RESULTS When the mean shear bond strength was compared within groups of the same configuration, there were no statistically significant differences. Comparison of the shear bond strength among groups of different configurations revealed statistically significant differences. The mean shear bond strength of composite onto 100% veneering ceramic surface and composite onto 50% veneering 50% all-ceramic cores was statistically higher than that of composite onto 100% all-ceramic cores; however, the differences of the shear bond strength of composite bonded only onto the veneering ceramic surface were not statistically significant from those of 50% surface area of composite bonded onto all-ceramic cores. CONCLUSION No statistically significant differences in the bond strength of a porcelain repair system to alumina and zirconia copings were observed. Increasing the surface of veneering ceramics to a porcelain repair system improved the repair materials bond strength.

Innovative approach to computer-guided surgery and fixed provisionalization assisted by screw-retained transitional implants.

PURPOSE The objectives of this case series are to describe a novel clinical approach to treat completely edentulous patients and determine its viability. Computer-guided implant planning was used to create a screw-retained surgical template (ST) supported by transitional implants and a fixed screw-retained provisional prosthesis supported by the transitional implants at the time of definitive implant placement. MATERIALS AND METHODS Five patients with at least one edentulous arch were treated. After the diagnostic tooth setup was performed, a duplicate with radiopaque acrylic resin was fabricated to serve as a surgical template (ST) for the placement of screw-form transitional implants and a radiographic guide (RG). Four transitional implants were strategically placed through the guide where they would not interfere with the future definitive implants. The transitional implants were used to support the RG during computed tomographic scanning. Subsequently, the RG was converted into a second ST based on three-dimensional virtual planning. Eight implants were placed by the computer-guided system, and an immediate prefabricated fixed provisional was connected to the transitional implants. RESULTS All the implants included in the study achieved primary stability and osseointegrated successfully. For 4 months, the transitional implants served successfully as abutments for the provisional prosthesis. CONCLUSION This innovative clinical approach overcomes the limitations of a mucosa/bone-supported ST by offering fixed, reproducible support for the RG and ST by means of transitional implants. The delivery of a prefabricated screw-retained provisional on transitional implants allows for passive healing and minimum chairside adjustments.

Guided Immediate Implant Placement with Wound Closure by Computer-Aided Design/Computer-Assisted Manufacture Sealing Socket Abutment: Case Report

Digital technology has been widely used in the field of implant dentistry. From a surgical standpoint, computer-guided surgery can be utilized to enhance primary implant stability and to improve the precision of implant placement. From a prosthetic standpoint, computer-aided design/computer-assisted manufacture (CAD/CAM) technology has brought about various restorative options, including the fabrication of customized abutments through a virtual design based on computer-guided surgical planning. This case report describes a novel technique combining the use of a three-dimensional (3D) printed surgical template for the immediate placement of an implant, with CAD/CAM technology to optimize hard and soft tissue healing after bone grafting with the use of a socket sealing abutment.

Fracture Resistance of CAD/CAM-Fabricated Lithium Disilicate MOD Inlays and Onlays with Various Cavity Preparation Designs: Fracture Resistance of CAD/CAM Lithium Disilicate

PURPOSE To examine the fracture resistance of premolars restored with CAD/CAM lithium disilicate mesio-occlusal-distal (MOD) inlays and onlays of different cavity designs. MATERIALS AND METHODS Two widths of occlusal isthmus (75%, 100% of intercuspal distance) and three designs of cuspal coverage (none, palatal, complete) were used for the preparation of MOD inlays and onlays in the extracted maxillary premolars. Sixty lithium disilicate restorations were milled and bonded into the cavities. After 24 hours of water storage, the specimens were loaded until fracture, and the fracture loads (N) were measured. Any evidence of cracks and fractures on the tested specimens were examined to classify failure patterns. RESULTS Mean fracture load values for the tested groups were as follows: 664.4 ± 214.7 N (group A), 659.3 ± 391.2 N (B), 681.9 ± 258.1 N (C), 938.1 ± 862.0 N (D), 841.7 ± 375.4 N (E), and 994.2 ± 486.3 N (F). The width of occlusal isthmus did not significantly affect the fracture loads among all the groups. Within groups with identical isthmus width, the fracture loads showed no significant difference depending on the designs of cuspal coverage. The majority of specimens showed either type III or IV fracture mode. CONCLUSIONS Within limitations of this study, the bonded restorations of premolars with CAD/CAM-generated lithium disilicate were reliable, regardless of cavity preparation design.

Occlusal Pressure Redistribution with Single Implant Restorations: Occlusal Pressure Following Implant Restorations

PURPOSE To describe the occlusal pressure redistribution in dental arches following placement of single posterior implant-supported restorations in occlusion with natural dentitions. MATERIALS AND METHODS Fifteen patients who presented for successfully osseointegrated single posterior implant restorations participated in the study. Cement-retained, all-ceramic implant crowns were fabricated and delivered after adjustment for interproximal contacts, fit, and uniform occlusal contacts. Occlusal pressure distribution was recorded with a digital sensor that reported contact point forces as a percentage of total pressure applied to the sensor. Measurements were taken before and after restoration for comparison. The distribution of relative occlusal stress was analyzed for statistical significance by location. RESULTS The results indicated that placement of posterior implant-supported restorations increased the bite pressure in the sextants containing the restorations by an average of 4.18% (p = 0.019) of the maximum value registered (maximum bite pressure). The contralateral occlusal load was found to decrease by 2.9% (p = 0.047) of the maximum value registered; however, there was no significant difference among or between the tooth positions. CONCLUSION Single posterior implant-supported restorations significantly increased the percentage (%) of total occlusal pressure in the containing sextant and decreased percentage of total occlusal pressure in the contralateral sextant. When analyzing restorations by exact position, more posterior implant restorations decreased the occlusal pressure applied in anterior dentitions.

Occlusal Pressure Redistribution with Single Implant Restorations

PURPOSE To describe the occlusal pressure redistribution in dental arches following placement of single posterior implant-supported restorations in occlusion with natural dentitions. MATERIALS AND METHODS Fifteen patients who presented for successfully osseointegrated single posterior implant restorations participated in the study. Cement-retained, all-ceramic implant crowns were fabricated and delivered after adjustment for interproximal contacts, fit, and uniform occlusal contacts. Occlusal pressure distribution was recorded with a digital sensor that reported contact point forces as a percentage of total pressure applied to the sensor. Measurements were taken before and after restoration for comparison. The distribution of relative occlusal stress was analyzed for statistical significance by location. RESULTS The results indicated that placement of posterior implant-supported restorations increased the bite pressure in the sextants containing the restorations by an average of 4.18% (p = 0.019) of the maximum value registered (maximum bite pressure). The contralateral occlusal load was found to decrease by 2.9% (p = 0.047) of the maximum value registered; however, there was no significant difference among or between the tooth positions. CONCLUSION Single posterior implant-supported restorations significantly increased the percentage (%) of total occlusal pressure in the containing sextant and decreased percentage of total occlusal pressure in the contralateral sextant. When analyzing restorations by exact position, more posterior implant restorations decreased the occlusal pressure applied in anterior dentitions.