[Computer design of artificial tooth series of complete removable prostheses]

The active development and introduction of CAD/CAM technologies in dental practice initiated the authors (of the article) to develop the algorithm of virtual set up of complete removable prostheses using 3D visualization system of face and dentitions. Patient's faces and individual tablespoon with occlusal rollers were scanning. Three-dimensional models ware received on. Then both models were put in correspondence with each other by software RapidForm 2006 Basis . Virtual artificial teeth were selected from computerized databank.

Comparison of computer generated occlusal surfaces with functionally waxed-on surfaces

CAD/CAM methods are also being used ever more frequently to produce fully anatomical restorations. These automated, computer-assisted methods play an outstanding role in generating occlusal surfaces. This study examines whether such computer generated occlusal surfaces are comparable with those which an experienced dental technician functionally waxes-up in the individually controlled articulator. A comparison of the occlusal surfaces in twelve posterior teeth of eleven functionally healthy patients showed differences ranging from 380 to 530 pm related to the mean difference in volume between both types of occlusal surface. Furthermore, a mean pixel deviation of the superimposed occlusal surfaces of 5.12 +/- 1.951 microm (min: 2.49 microm, max: 9.16 microm) was observed. These deviations were found for both functionless surfaces and occlusal surface areas of the functional occlusion. Thus, comparable occlusal surfaces can be achieved with computer generated methods, but they do not quite achieve the result of functionally waxed-up occlusal surfaces in the individually programmed articulator.

[Prosthetic rehabilitation of patients with parodontitis based upon the use of 3D-technologies--clinical case example]

Clinical case of prosthetic rehabilitation of patient (female) with generalized parodontitis complicated by defects and deformations of dentitions was offered. Using 3D-technologies position of teeth was corrected with the help of a series of temporary transparent splints-modifiers with subsequent guy splintage and esthetic 3D-planning of front teeth forms. Teeth forms correction was made by composite using preliminary prepared templet.

Esthetic rehabilitation of worn anterior teeth with thin porcelain laminate veneers

Bonded porcelain restorations are a predictable and durable treatment option with which not only esthetic appearance but also the strength and function of teeth can be re-established. One of the most important issues of today's dentistry is the preservation of sound enamel. Following biomimetic principles, employing minimally invasive applications and adhesive technologies are of paramount importance for successful restorations. The mock-up technique is advised for delicate removal of the required space for thin porcelain veneers minimally. Besides minimally invasive preparation, long-term success is determined by the adhesive quality of the laminate veneers. This case presentation demonstrates restoration of anterior dentition where the wear of incisal edges posed a negative effect on the smile of the patient. Before bonded porcelain veneers were adhesively cemented, incisal lengthening with direct resin composite and gingival contouring was performed. By using the mock-up technique, minimal preparations were made with the outline ending in enamel only. For cementation of these restorations, step-by-step adhesive procedures are presented.

[Use of computer 3D-technologies on the stage of planning and realization of dental implantation]

It was shown that with the help of preliminary esthetic planning based upon computer 3D-visualization of implantation was realized with subsequent prosthetic treatment. One could receive the planned result by combining different 3D-technologies based upon suitable program and hardware with open platform.

Influence of CAD/CAM scanning method and tooth-preparation design on the vertical misfit of zirconia crown copings

PURPOSE

To evaluate the influence of scanning method, finish line type and occlusal convergence angle of the teeth preparations on the vertical misfit of zirconia crown copings.

METHODS

20 standardized stainless-steel master dies were machined simulating full-crown preparations. The total convergence angle was 15 degrees or 20 degrees (n=10 each). Two of the finish line types: a chamfer (CH) and a shoulder (SH) were prepared around the contour of each abutment. Over these dies, 20 structures were made by CAD/CAM (Cercon, Dentsply). An optical laser digitized the wax patterns of 10 single-unit copings (WS), and 10 abutments were direct-scanned to design the cores by computer (DS). Zirconia milled caps were luted onto the models under constant seating pressure. Vertical discrepancy was assessed by SEM. Misfit data were analyzed using ANOVA and Student-Newman-Keuls (SNK) test for multiple comparisons at alpha = 0.05.

RESULTS

Vertical gap measurements of WS copings were significantly higher than those of DS frames (P < 0.0001). SH exhibited statistically higher discrepancies than CH when combined with a 15-degree occlusal convergence angle regardless of the scanning method (P < 0.05). The taper angle of the preparation (15 degrees vs. 20 degrees) had no effect on the marginal adaptation of chamfered samples.

Technique for making full-coverage provisional restorations on teeth with insufficient clinical crowns

Provisional restorations fabricated with copper bands are tremendous practice builders, eliminating the sensitivity, recurrent decay and poor retention that are common with conventional temporary restorations. The copper-band provisional restoration is the ideal choice when conventional butt-joint temporary restorations are unsuitable. The technique for making this restoration is demonstrated in this article with a step-by-step "how-to" description. An analysis of the basic principles and theories behind the success of the copper band provisional restoration is also presented, as well as a discussion of the restoration's advantages and disadvantages.

Immediate loading of the edentulous maxilla with a definitive restoration supported by an intraorally welded titanium bar and tilted implants

PURPOSE

The aim of this prospective study was to evaluate the concept of intraoral welding as a suitable technique for the fabrication of a restoration for the edentulous atrophic maxilla on the day of placement of axial and tilted implants.

MATERIALS AND METHODS

Thirty patients received three axial and four tilted implants in the edentulous maxilla. Immediately after implant placement, definitive abutments were connected to the implants and then a titanium bar was welded to them using an intraoral welding unit. This framework was used as a support for the definitive restoration, which was attached on the day of implant placement. Mean marginal bone loss and radiographically detectable alteration of the welded framework were assessed using periapical radiographs immediately after surgery and at 6, 12, 24, and 36 months after placement.

RESULTS

Sixteen men and 14 women with an average age of 58.1 years (SD 13.6) were consecutively treated with 210 immediately loaded implants. No fractures or radiographically detectable alterations of the welded frameworks were evident. A 100% prosthetic success rate was seen at 36 months. Three (1.4%) implants had serious biologic complications, resulting in success rates of 97.8% for axial implants and 99.2% for tilted implants. The accumulated mean marginal bone loss was 0.92 mm (SD 0.75; n = 90) for axial implants and 1.03 mm (SD 0.69; n = 120) for tilted implants. The average pocket probing depths were 1.87 mm (SD 0.98; n = 90) for the axial implants and 1.95 mm (SD 0.81; n = 120) for the tilted implants.

CONCLUSIONS

It is possible on the day of implant placement surgery to successfully rehabilitate the edentulous atrophic maxilla with a fixed, definitive restoration supported by an intraorally welded titanium framework attached to axial and tilted implants.

Implant verification cast--a predictable restorative system in implant prosthodontics

An implant verification cast is designed to provide an accurate representation of dental implant positions extraorally. It can be used by the laboratory as a trusted cast to create a passively fitting framework and by the clinician to verify framework fit prior to intraoral trial. This article discusses the treatment philosophy behind this specific cast and reviews applications, fabrication techniques and benefits of the verification cast compared to the conventional technique.

In vitro evaluation of marginal adaptation in five ceramic restoration fabricating techniques

OBJECTIVE

To compare in vitro the marginal adaptation of crowns manufactured using ceramic restoration fabricating techniques.

METHOD AND MATERIALS

Fifty standardized master steel dies simulating molars were produced and divided into five groups, each containing 10 specimens. Test specimens were fabricated with CAD/CAM, heat-press, glass-infiltration, and conventional lost-wax techniques according to manufacturer instructions. Marginal adaptation of the test specimens was measured vertically before and after cementation using SEM. Data were statistically analyzed by one-way ANOVA with Tukey HSD tests (a = .05).

RESULTS

Marginal adaptation of ceramic crowns was affected by fabrication technique and cementation process (P < .001). The lowest marginal opening values were obtained with Cerec-3 crowns before and after cementation (P < .001). The highest marginal discrepancy values were obtained with PFM crowns before and after cementation.

CONCLUSION

Marginal adaptation values obtained in the compared systems were within clinically acceptable limits. Cementation causes a significant increase in the vertical marginal discrepancies of the test specimens.

Effect of CAD-CAM porcelain veneers thickness on their cemented color

OBJECTIVE

To determine the effect of thickness of porcelain veneers constructed from CAD-CAM on their final color when two resin cements were used.

METHODS

Buccal surfaces of extracted sound human molars with shade 3M2 [verified using digital spectrophotometer (Vita Easyshade-Vident)] were reduced to expose flat enamel surfaces. CAD-CAM blocks (Vitablokcs Mark II) of the same shade were sectioned into three groups of 0.3, 0.5 and 0.7mm thickness. Each group was subdivided into two subgroups; one subgroup was cemented to enamel using an etch-and-rinse resin cement (Calibra/Prime and bond-NT, Dentsply) and the other was cemented to enamel using a self-etching resin cement (Panavia-F, Kuraray). The shade of the two resin cements was "light". Change in color (ΔE) between the selected shade (3M2) and the resulted shade was measured for each specimen using a digital spectrophotometer (Vita Easyshade-Vident). Means and SDs were calculated and data was statistically analyzed using ANOVA and post hoc tukey's.

RESULTS

Change in color (ΔE) between the selected and the produced shade for the Calibra subgroups was 2.8 (0.3) for the 0.3mm, 1.67 (0.2) for the 0.5mm thick specimens and 1.26 (0.3) for the 0.7mm. Panavia F subgroups showed ΔE of 2 (0.4) for the 0.3mm, 1.13 (0.23) for the 0.5mm thick specimens and 1.21 (0.31) for the 0.7mm. The 0.7mm subgroups showed no significant difference in color change among the two cements (P>.05), however, Calibra resulted in significantly higher change in color values for the 0.5mm thick specimens (P<.05). In spite of the presence of significant difference for the Calibra 0.5mm thick subgroup, the color change was considered to be within the clinically acceptable range. The 0.3mm showed high significant difference for the two tested cements with the Panavia showing less change in color and Calibra showing clinically detectable change in color.

CONCLUSION

Increasing porcelain veneer thickness from 0.5 to 0.7mm did not significantly affect the final color of cemented veneers. Whilst the color was significantly affected at the thickness of 0.3mm.

[Computer aided design and manufacture of the removable partial denture framework]

This paper demonstrates the successful application of a novel approach to the computer aided design (CAD) of removable partial denture (RPD) framework. Firstly, we get the data of the partially edentulous cast, a mandibular Kennedy Class II, through a 3D-optical grating measuring system after corresponding pretreatment. Then, the reverse engineering software and 3D CAD software was used to design basis, big conjunction, clasp, small conjunction of the RPD framework. Finally 3D surface model of the RPD framework was created in preparation for direct manufacture using rapid prototyping (RP) methods and foundry. The result indicated that the RPD framework was fabricated successfully and the resulting frameworks provided a satisfactory fit.

The occlusal precision of laboratory versus CAD/CAM processed all-ceramic crowns

PURPOSE

The null hypothesis was tested: There is no difference between two all-ceramic crown systems, the Cerec method (CHAIR) and the IPS Empress method (LAB), with respect to occlusal precision and time expenditure for the dentist.

METHODS

20 casts representing clinical situations were mounted in semi-adjustable articulators to serve as simulation models. The left lower first molars were prepared to receive feldspathic ceramic crowns. The minimum number of three (Min3) occlusal contacts and their desired location was defined on each crown before preparation. Two crowns were produced on each die: (CHAIR) was applied in order to simulate a chair-side treatment and [LAB] was applied to simulate the laboratory/clinical mode of production. Additionally the time required to perform the occlusal adjustment was measured. For occlusal analysis, the (Min3) were divided by the contacts that were "actually achieved" (ACT). Mean quotients for (LAB) and (CHAIR) were calculated (n = 20 each). The Wilcoxon signed rank test at P < or = 0.05 was applied to determine statistical significance.

RESULTS

The mean quotients MEAN QU (Min3)/(ACT) of 0.87 for (CHAIR) and 0.94 for (LAB) and the time expenditure for simulating intraoral occlusal adjustment of 3.44 minutes for (CHAIR) and 3.79 minutes for (LAB) did not differ significantly.

[Occlusal overload--a risk factor in implant based prostheses]

The aim of the study was to perform a review of the literature data in regard to the main causes leading to failure of the dental implants and subsequently, of the implant based prostheses. Besides biological risk factors as infection, occlusal overload is considered the main mechanical risk factor being responsible for weakening or fracturing of the fixation screws, fracturing of the prosthesis or even of the implants. Understanding the fundamental differences between the natural dental structures and the implants may lead to a rigorous occlusal control as a key factor to success of implant born prosthesis. Among these, the periodontal ligament is of outmost importance because it allows a physiological-functional adjustment of occlusal stress in the longitudinal axis of the natural teeth and adaptation to the occlusal stress changes. In conclusion, the absence of periodontal ligament may lead to occlusal overload and implant failure due to lack of adjustment of occlusal forces intensity and axial transmission of these forces, as well as the absence of periodontal proprioceptors.

The evaluation of selected attachment systems for implant-retained overdenture based on retention characteristics analysis

The results of mechanical characteristics of attachments used for retaining and stabilizing overdenture have been analysed. Two commercially used attachments (a ball attachment and a bar attachment) and elastic frictional attachments designed by the research team with Professor Chladek as the leader have been investigated. The diagrams of force-displacement characteristics have been registered. Retention forces (F(R)) have been determined and total work (W(T)) disconnecting the attachments has been calculated on the basis of these diagrams. The analysis of total work corresponding to different types of attachments made it possible to distinguish some characteristic areas which illustrate specific features of particular designs. It has been revealed that determining the retention force allows us to compare only the attachments which work on similar bases. In order to conduct a purely objective comparison of the efficiency of different designs, it is necessary to analyze complete force-displacement characteristics as well as to determine on this basis the subsequent phases of separating the parts of attachments and to find the value of the work which in fact determines their quality. The comparison of selected commercially used designs and the presented elastic frictional attachments (taking into account the criterion of work) gives clear evidence that the introduced design of attachment enables us to create very good conditions of retaining overdenture.

[Use of computer technologies in prosthetic treatment of patients with front teeth loss]

Use of the proposed computer modeling technology with taking into account the individual face size based upon multivariate statistical analysis with the possibility of art editing during the final stage of modeling let to take into consideration individual peculiarities of face structure and gender differences and to recreate individual form and sizes of front artificial teeth for non removable prosthetics. The results of computer modeling use in prosthetic treatment of patients with front teeth loss and the results of comparison with traditional method and also with preliminary use of computer modeling were demonstrated.

Accuracy of occlusal contacts for crowns with chairside CAD/CAM techniques

Information from the opposing dentition is used to design and fabricate occlusal contacts with a reasonable level of accuracy for a given restoration. The dental database with the antagonist design process utilizes a bite registration to propose the construction of a virtual opposing model. The Articulation design technique utilizes a functionally generated bite registration to control both the maximum intercuspation and excursive contacts on the restoration. Correlation design technique offers the opportunity to copy the established occlusal anatomy to the preparation. Although these techniques offer a workflow to establish occlusal contacts with the Cerec system, there is a lack of quantitative data as to the accuracy achieved. Alternative techniques to control the occlusal contacts have been suggested which rely on "user customized design techniques" that recommend altered program settings, manual override of automated features in the software, or modification of the established software design programs. The purpose of this study was to measure the occlusal vertical discrepancy for various design techniques. Full crowns made using dental database with the antagonist design technique had a significantly smaller occlusal vertical discrepancy than those made with correlation. Dental Database with the Antagonist had a significantly smaller occlusal vertical discrepancy than all suggested alternative design techniques. Use of the Dental Database with Antagonist design technique provides the most accurate technique for establishing occlusal contacts with the Cerec 3D system.

The parallel stratification masking technique: an analytical approach to predictably mask discolored dental substrate

Discolored dental substrates continue to challenge the restorative team when ultraconservative treatment modalities are chosen. An innovative laboratory concept--the parallel stratification masking technique--has been developed in order to achieve maximum preservation of dental hard tissues and predictably accomplish a desirable esthetic outcome. The major advantages of this technique are that the ceramist is able to: a)identify and map the discolored dental substrate, b)predictably mask the discolored dental substrate, and c) assess the appropriate masking efficacy of the fabricated restoration prior to laboratory delivery to the dentist in cases of bonded porcelain restorations.

Load transfer by fine threading the implant neck--a FEM study

Osseointegration of dental implants up-to-date is a well-confirmed phenomenon, however the long-term stability and integrity of the bone and soft tissue collar is under discussion. A homogenous distribution of the bone loading is a prerequisite for bone modelling and preservation in the neck area while overload must be avoided. Based on the finite element method (FEM) models of implants without and with a fine thread (implant types Tiolox and tioLogic) with surrounding bone were generated and analysed using the FE program system MSC.Marc/Mentat. The alveolar bone was considered to be an idealized segment with a cortical bone thickness of 2 or 3 mm, respectively with an enclosed spongy bone. The implants were loaded with forces up to 300 N in two different directions, in the first case with a purely vertical force and in other case with an additional lateral force component with a angle of 45 degrees with respect to the occlusal plane. The deflections of the implants ranged from 0.004 to 0.017 mm in the load direction, depending on the implant diameter and the cortical bone thickness. When considering a physiological vertical load of a maximum of 100 N, the highest strains were about 2100 micro strain in the spongy bone. Within the fine thread in the neck area of the implant, the maximum stresses were increased in the cortical bone by 3%. The improvement of implant anchorage in the cortical bone reduced the strains in the spongious bone, at the same time there were no additional stress peaks visible at the fine thread region.

Biomechanical evaluation of implant placement in the reconstructed mandible

PURPOSE

Following resection of malignant tumors from the mandible, immediate reconstruction of the discontinuous jaw is commonly performed. The present study aims to define the risks associated with dynamic loading of the reconstructed mandible.

MATERIALS AND METHODS

Computer-aided design simulations of eight mandibles were produced and termed normal models. The normal models were then modified by removing part of the right body and restoring the defects with bone from the rib or fibula. These modified models were termed reconstructed models. Thereafter, an implant was embedded in the first molar region of the left side for all models. Using finite element analysis, the stresses occurring at the implant-bone interface with simulated mastication were calculated. The Wilcoxon signed rank test was applied to compare the magnitudes of stresses in both models.

RESULTS

In terms of the stress exerted at the implant-bone interface during mastication, the normal models and the reconstructed models showed no significant differences (P > .05).

CONCLUSION

Placement of an implant on the nonreconstructed side following partial resection and mandibular reconstruction presents no significant risk.