In vitro measurement of the retention force of two stud attachment systems during cyclic load.

PURPOSE: To investigate the retentive behavior of the Locator legacy and Novaloc attachment systems with different retention inserts both within and across systems under cyclic load. MATERIALS AND METHODS: Three retention inserts of each system (green, yellow, and white for Novaloc; green, orange, and red inserts for extended range for legacy Locator) were tested on abutments of both systems with a sample number of 10 per force and 10,000 cycles of insertion and removal. The loading was applied in the axial direction of the abutments, which were placed in artificial saliva. The retention force was measured in each cycle. The results were compared with the manufacturer's specifications and evaluated for a simulated period of use of 10 years. Characteristic time constants were determined, and subsequently, the two systems were compared regarding their wear behavior. RESULTS: The manufacturer's specifications could only be confirmed for the green Novaloc retention insert on a Novaloc abutment (t-test: p = 0.50); for all other inserts, the baseline exceeded the manufacturer's specifications by 30%-75% (Novaloc; t-test: p < 0.001) and 75%-550% (Locator; t-test: p < 0.001). After 10,000 cycles performed, the manufacturer's specifications were confirmed on a Novaloc abutment for the white Novaloc retention insert (t-test: p = 0.86) and on a Locator abutment for the green Novaloc retention insert (t-test: p = 0.32). Both systems lost retention force during the experiment. Overall, Novaloc inserts on both abutments showed less wear (decrease to 56%-85% of initial force) and a slower decrease in retention force compared to Locator inserts (decrease to 6%-31% of initial force). CONCLUSIONS: In both systems, wear leads to a varying loss of retention; therefore, regular checks with possible replacement of the inserts are necessary in clinical use. Novaloc attachments seem to be more resistant to the loss of retention than Locator attachments. A cross-combination may be clinically useful in some cases.

Comparison of the Accuracy of a Mounting Fixture for Dental Implants for Implant Position Transfer and Open-Tray Implant Level Impression-An In Vitro Study.

The accuracy for the implant position transfer of a mounting fixture and a standardized open-tray implant level impression was compared. Ten aluminum master models with four implant analogs placed in different angulations were fabricated. By performing an open-tray implant level impression stone casts were produced. The master models and stone casts were scanned (comparison group one) using a laboratory scanner. Deviations in the scan body surface were determined in the form of mean (absolute) point distances and (signed) surface distances. The same procedure was performed with a screwed transfer and by fixing the posts of the mounting fixture (comparison group two). The mounting device was applied to each master model and scanned in a fixed and detached state (comparison group three). In a point comparison, the open-tray implant level impression showed mean deviations of 43.6 µm and a mounting fixture of 44.6 µm with no significant differences (p < 0.05). There were significant differences between groups two and three. The angulation of the implants had no effect on the accuracy. In a surface comparison, the open-tray implant level impression showed mean deviations of 36.0 µm and a mounting fixture of 2.0 µm (p > 0.05). Within the limits of this study, the mounting fixture transferred the implant position with the same accuracy as the open-tray implant level impression with respect to point deviations.

Cross Sectional Analysis of Eurasian Skull Anatomy for 3D Cephalometry-Normative Data Reveal Four Different Skull Types.

The unsolved problem in three-dimensional surgical planning for patients with facial deformity, dysgnathia, or asymmetry is the lack of a normative database of "norm skulls" that can be used as treatment objectives. A study was conducted on 90 Eurasian persons (46 male and 44 female adults) for whom cone beam-computed tomography images were available. Inclusion criteria were adult patients with a skeletal Class I pattern, proper interincisal relationship with normal occlusion, the absence of an open bite both in the anterior and posterior region, and a normal and balanced facial appearance; patients with dysgnathia and malformations were excluded. A total of 18 landmarks were digitized and 3D cephalometric measurements were performed and analyzed by means of proportions calculated from the landmarks. Male and female skulls were analyzed, as well as subdivisions revealed by cluster analysis. The data showed that four subtypes of skulls were distinguishable with statistical significance (p < 0.05). A male and a female type subdivided in a brachiocephalic and dolichocephalic phenotype could be identified. For each type, a mean shape was calculated by a Procrustes transformation, which, in turn, was used to create four template skulls from a male and a female skull. This was accomplished by fitting the polygon models of the two skulls to each of the two subtypes based on the landmarks marked on them using a thin plate spline transformation. The normative data of the subtypes can individually serve as a guide for orthodontic surgery in the Eurasian population, which is especially helpful in 3D planning and the execution of craniofacial operations.

Assessment of facial and cranial symmetry in infants with deformational plagiocephaly undergoing molding helmet therapy.

OBJECTIVES: The aim of this study was to determine the effects on facial and cranial symmetry through molding helmet therapy in infants with positional plagiocephaly. A 3D asymmetry index (3DAI), which measures both cranial and facial symmetry, was introduced and compared to the Cranial Vault Asymmetry Index (CVAI). MATERIAL & METHODS: Optical 3D-scans of children with positional plagiocephaly were evaluated retrospectively. Pre- and post-therapeutic asymmetry values of the cranium and face were determined and paired t-tests were applied. Pearson correlations were calculated for facial and cranial asymmetries. RESULTS: 65 children (age: 3-6 months) were included. Asymmetry values (mean/standard deviation, pre- and post-therapeutic) were for 3DAI determinations: cranium: 9.96/1.84-8.11/1.74 p < 0.001; face: 4.70/1.06-3.89/0.91 p < 0.001; and for CVAI measurements: 9.10/3.29-5.88/2.78 p < 0.001. No correlation was found between facial and cranial asymmetry (p > 0.05). CONCLUSION: Symmetry values improved significantly in post therapeutic 3D-scans for both asymmetry indices. The analysis of cranial symmetry by 3DAI should be preferred over the CVAI because it gives more comprehensive information, including the symmetry of the entire cranial surface and the face.

Facial and midfacial symmetry in cleft patients: Comparison to non-cleft children and influence of the primary treatment concept.

PURPOSE: Patients with cleft lip, alveolus and palate (CLAP) may suffer from marked asymmetry with an impact on attractiveness and psychosocial aspects. The aim of this study was to assess symmetry in CLAP patients compared to non-cleft controls of similar age with regard to cleft type and treatment concept. MATERIALS AND METHODS: In CLAP patients with different cleft forms and in healthy non-cleft subjects (control group) a three-dimensional stereophotogrammetric face scan was performed and an objective 3D asymmetry index (AI) was calculated for the whole face, the midface, the upper lip and the nose. RESULTS: In total, 305 patients were included: 140 CLAP patients (90 male, 50 female, mean age 9.9 ± 3.6 years) and 165 controls (87 male, 78 female, mean age 8.7 ± 2.1 years). In general, CLAP patients showed significantly higher asymmetry than controls, with the most severe asymmetry found in unilateral complete CLAP. Patients treated according to an actual concept considering reconstruction of all affected muscular systems had a significant lower and more favourable AI than patients not treated according to this concept (p < 0.05). CONCLUSION: An adequate treatment concept is essential to achieve better results concerning symmetry in CLAP, but symmetry values of healthy non-cleft controls are not reached.

Computer-aided design of facial prostheses by means of 3D-data acquisition and following symmetry analysis.

The aim of this study was to investigate whether a method of designing digital models of facial prostheses was suitable for patients with orbital defects. 32 patients were included in a retrospective study. 23 of them already had a facial prosthesis. 3D-data of the faces were acquired optically using fringe projection technique without and with (if available) the facial prosthesis in place. The healthy side of the surface models was mirrored to reconstruct the defect area. By generating a NURBS-model, the edges of the virtual prostheses were adapted to the defect region. The CAD models were stored in STL format as templates for facial prostheses. Using an automatically calculated asymmetry index (AI), four situations of the digitized facial surface were analysed for symmetry: 1. with defect area excluded, 2. with mirrored healthy surface, 3. with digital CAD template, and 4. with manually produced facial prosthesis inserted (if available). Mean AI values were 6.05 ± 3.26 (situation 1), 4.79 ± 2.51 (situation 2), 5.12 ± 2.61 (situation), and 6.74 ± 2.77 (situation 4). Additionally, the CAD templates were rated by three anaplastologists. Ratings did not differ significantly. They partially agreed with the three statements "The CAD prosthesis fits harmoniously within the face", "The CAD prosthesis could be used for a wax pattern during conventional fabrication" and "The CAD prosthesis and the wax pattern reduce workload". The results indicate that the presented technique has the potential to increase facial symmetry and facilitate the technical procedure. However, symmetry alone is not a sufficient criterion for design of a facial prosthesis.

Measured symmetry of facial 3D shape and perceived facial symmetry and attractiveness before and after orthognathic surgery.

One aim of cranio-maxillo-facial surgery is to strive for an esthetical appearance. Do facial symmetry and attractiveness correlate? How are they affected by surgery? Within this study faces of patients with orthognathic surgery were captured and analyzed regarding their symmetry. A total of 25 faces of patients were measured three-dimensionally by an optical sensor using the fringe projection technique before and after orthognathic surgery. Based upon this data an asymmetry index was calculated for each case. In order to gather subjective ratings each face was presented to 100 independent test subjects in a 3D rotation sequence. Those were asked to rate the symmetry and the attractiveness of the faces. It was analyzed to what extend the ratings correlate with the measured asymmetry indices and whether pre- and post-surgical data differ. The measured asymmetry indices correlate significantly with the subjective ratings of both items. The measured symmetry as well as the rated symmetry and attractiveness increased on average after surgery. The increase of the ratings was even statistically significant. A larger enhancement of symmetry is achieved in pre-surgical strongly asymmetric faces than in rather symmetric faces.

Measuring facial symmetry: a perception-based approach using 3D shape and color.

OBJECTIVE: Facial symmetry is an important factor affecting esthetics. Thus, its restoration is an essential task in maxillofacial surgery. The aim of this study is to develop an objective measure of facial asymmetry by a novel approach where both the shape and the color are taken into account and to validate its correlation with perception. METHODS: Optical three-dimensional (3D) face scans of 30 healthy adults are performed. Face-specific asymmetry indices are calculated by quantifying color differences as well as spatial distances between 3D data of a face and its mirrored copy. Subjective ratings of symmetry and attractiveness of the faces by 100 subjects are used to validate these indices. RESULTS: The symmetry ratings show significant correlations with color and geometric asymmetry indices. The attractiveness ratings correlate only weakly with both indices. However, the product of the indices exhibits significant correlations with both attractiveness and symmetry ratings. CONCLUSION: The presented combined asymmetry index comprising shape and coloring turned out to reflect subjective perception of both facial symmetry and attractiveness. It thus promises to be a valid objective measure for facial esthetics, which could contribute, e.g., to the evaluation of surgical methods as well as to the design of craniofacial prostheses.

2D and 3D analysis methods of facial asymmetry in comparison.

Symmetry is a significant factor, among others, influencing the attractiveness of human faces. Hence its restoration is an essential task in oral and maxillofacial surgery. Until recently, most of the techniques to objectively quantify the facial asymmetry were based on the evaluation of two-dimensional data, i.e. photographs. These techniques are well-established in literature and have in common that several landmarks in the face are identified manually and put together in a formula to obtain a facial asymmetry value. The increasing availability of three-dimensional measuring systems offers the possibility to perform an automated 3D analysis of the facial symmetry based on a dense 3D point cloud of the facial surface. The results of this analysis are on the one hand a mirror plane, which meets best the partial symmetry of the face regarding the median sagittal plane, and on the other hand a 3D asymmetry index quantifying the overall facial asymmetry characteristics. In this paper three selected 2D analysis methods and one 3D analysis method are compared.

Quantification of facial asymmetry by 2D analysis - A comparison of recent approaches.

INTRODUCTION: Symmetry has been found to play a crucial role in attractiveness assessment and so its restoration is an essential problem in oral maxillofacial surgery. This paper presents an overview of recent 2D asymmetry analysis techniques. These are techniques which are based on the evaluation of two-dimensional data, like photos. The aim of this paper is to find the most precise and practical techniques to investigate facial asymmetry. MATERIALS AND METHODS: For this purpose studies addressing symmetry investigations are collected and categorized by the type of data they extract from the photos. The reference points on the facial surface, which are frequently used in these studies, are presented and calculation methods are described. RESULTS: Three kinds of techniques using vertical or horizontal reference lines or centres of bilateral points appear to be most appropriate. Recommendations are made, which aspects should be taken into account when calculating symmetry/asymmetry indices from photos. Advantages and disadvantages of the three selected methods are summarized in a table. CONCLUSIONS: Using one of the three recommended approaches denoted by FA, AI and z-score allows calculating meaningful asymmetry values. The proper selection and identification of reference points is crucial. For highest accuracy, a sufficient number of evenly distributed and reproducible reference points should be used.

Image-based extracorporeal tissue engineering of individualized bone constructs.

PURPOSE: Computer-aided technologies have been recently employed for use in extracorporeal bone tissue engineering strategies. In this pilot animal experimental study, the intention was to test whether autologous osteoblast-like cells cultured in vitro on individualized scaffolds can be used to support bone regeneration in a clinical environment. MATERIALS AND METHODS: For this purpose, mandibular bone defects were surgically introduced into the mandibles of minipigs and the scaffold of the defect site was modeled by computer-aided design/computer-aided manufacturing technique. Autologous bone cells from porcine calvaria were harvested from minipigs and grown in culture. Cells were seeded on scaffolds generated by rapid prototyping of polylactic acid/polyglycolic acid copolymers. The defects were then reconstructed by implanting the tissue constructs. RESULTS: The intraoperative sites as well as the postoperative computerized tomographic scans demonstrated an accurate fit in the defect sites. The implanted scaffold constructs enriched with osteoblast-like cells were well tolerated and appeared to support bone formation, as revealed by histologic and immunohistochemical analyses. DISCUSSION: These results indicated that in vitro expanded osteoblast-like cells spread on a resorbable individualized scaffold can be capable of promoting the repair of bony defects in vivo. CONCLUSION: These results warrant further attempts to combine computer modeling and tissue engineering for use in bone reconstructive surgery.

Spectral analysis of /s/ sound with changing angulation of the maxillary central incisors.

PURPOSE: The aim of the study was to measure the influence of the maxillary central incisors free from adaptation phenomena using spectral analysis. MATERIALS AND METHODS: The maxillary dentures of 18 subjects were duplicated. The central incisors were fixed in a pivoting appliance so that their position could be changed from labial to palatal direction. A mechanical push/pull cable enabled the incisor section to be handled extraorally. Connected to the control was a sound generator producing a sinus wave whose frequency was related to the central incisor angulation. This acoustic signal was recorded on one channel of a digital tape recorder. After calibration of the unit, the denture duplicate was inserted into the subject's mouth, and the signal of the /s/ sounds subsequently produced by the subject was recorded on the second channel during alteration of the inclination angle simultaneously with the generator signal. Spectral analysis was performed using a Kay Speech-Lab 4300B. RESULTS: Labial displacement in particular produced significant changes in spectral characteristics, with the lower boundary frequency of the /s/ sound being raised and the upper boundary frequency being reduced. CONCLUSION: Maxillary incisor position influences /s/ sound production. Displacement of the maxillary incisors must be considered a cause of immediate changes in /s/ sound distortion. Therefore, denture teeth should be placed in the original tooth position as accurately as possible. Our results also indicate that neuromuscular reactions are more important for initial speech sound distortions than are aerodynamic changes in the anterior speech sound-producing areas.

Optical data acquisition for computer-assisted design of facial prostheses.

PURPOSE: The conventional impression technique for manufacturing facial prostheses has the disadvantage of deforming the soft tissues because of the tension caused by the impression material, as well as causing discomfort to the patient. The purpose of this study was to establish a system that allows contact-free reproduction of the facial surface combined with computer-assisted design and fabrication of facial prostheses. MATERIALS AND METHODS: Three-dimensional data of the facial surface were obtained using an optical acquisition system based on the method of phase-measuring profilometry. A sensor head with a fringe projector and two CCD cameras for photogrammetric triangulation were used in connection with a PC for measurement control and data evaluation. Software for computer-assisted design of the facial surface to be reconstructed was developed. A prototype facial prosthesis was fabricated using stereolithography. The system was tested using a modified puppet head. First clinical tests were performed with a patient who had undergone maxillofacial surgery including the resection of one eye. RESULTS: Three-dimensional data acquisition and imaging allow visualization of a whole face without causing tension or neuromuscular reaction. As surface brightness is also part of the digital model, it is even more realistic than a plaster cast. The stereolithographic object showed good marginal fit and satisfactory shape. CONCLUSION: The presented technique allows three-dimensional data reproduction of the facial surface, computer-assisted design of a facial prosthesis, and transfer to a rapid prototyping unit. The system has obvious advantages over conventional impression techniques. Further clinical trials are planned to evaluate the clinical success of the technique.

Bone loading pattern around implants in average and atrophic edentulous maxillae: a finite-element analysis.

Introduction: Oral implants placed in the maxilla, especially the posterior region, have a lower success rate than those placed in the mandible. Poor bone quantity and quality have been suggested as a reason for this differential success rate. Objective: The purpose of this study was, therefore, to evaluate stress and strain distributions around loaded implants in the normal and atrophic maxilla by finite-element (FE) analyses. Material: FE models of a solitary implant were generated to determine stresses and strains in the bone adjacent to the implant surface under loading conditions. Study design: Different bony situations and implant lengths were used in a FE model. Static loads were applied axially and the resulting stresses and strains calculated. Results: Bone quality and quantity play a major role in decreasing bone strains adjacent to the implant surface under loading. It was found that stresses were more homogeneously distributed when more spongy bone was present. Decreased bone height was found to have less pronounced effects on strain and stress alterations than poor bone quality. Atrophic bony dimensions in combination with poor bone quality were associated with surface strains exceeding physiological levels (>6000 microstrains). Conclusion: Our investigation indicates that supraphysiological bone strains adjacent to the implant surface should be expected under mechanical loading in the atrophic maxilla. Copyright 2001 European Association for Cranio-Maxillofacial Surgery.