Poster 9, Sprache: Englisch
Objectives: Two systems with different technologies for intraoral digital radiographs were evaluated in vitro and in vivo and compared to conventional dental X-rays.
Material and Methods: Spatial resolution was determined for all three systems. Picture noise and distortion effects of both digital systems were evaluated. The permanence of the stored information content was examined for the sensor plate (= storage phosphor). Additionally, rectangular bone blocks with inserted implants and artificial bone defects were exposed with all systems and the images were quantitatively evaluated. 79 digital radiographs of 51 patients served for the examination of the diagnostic relevance of the images in comparison to conventional dental X-rays of the same patients. All data were processed with professional statistical software (SAS for Windows, Release 6.12).
Results: Conventional film exhibited the best spatial resolution (20Lp/mm) followed by the CCD-sensor (11Lp/mm) and the sensor plate (8Lp/mm). Storage phosphor offered a wide dynamic range, but the information content underwent a distinctive increase in noise within 12 hours post exposure. Measurements of the defined bone defects were most precise with the CCD-system for both vertical and horizontal dimensions. On the other hand the CCD-sensor presented a considerably high image noise. Another drawback of the CCD-sensor was the rather complicate in vivo application compared to both conventional films and sensor plates.
Conclusions: Though the compared systems exhibited distinctive differences in the spatial resolution, this parameter had less impact on the quality of the images than picture noise and contrast. Both digital systems are considered to be appropriate for diagnostic purposes. However, comparing the two digital systems, the storage phosphor seems to be favorable for its easier handling, radiation reduction, and better imaging quality.
Schlagwörter: digital dental radiography, CCD sensor, storage phosphor, dose reduction
Poster 10, Sprache: Deutsch
Aim: In order to achieve anatomically correct measurements of the tooth axes in Dental CT, a standard evaluation framework is necessary because there is no possibility to fix the patient's head in CT.
Material: A macerated skull and 23 patients with full dentitions.
Methods: A macerated skull with a titan plate in the occlusal plane was scanned in four different positions. In this presentation an example is given by the images of the skull tilt 7° to the left. In the first step the angulations of the teeth were measured to the horizontal edge of the panoramic and paraxial CT reformations (original measurements). These values were entered into a self developed angulation correction program based on a defined reference compared with the original measurements and with the values which were obtained by plane (occlusal plane). The corrected values were then measuring the angle between the tooth axes and the titan plate (control measurements). The results were analysed statistically. In addition, the Dental CT images of 23 patients partly with misplaced teeth were analysed analogously.
Results: For the macerated skull the difference between the corrected values and the control measurements was up to 1°. However the difference between the original measurements and the corrected values was up to 7°. In the panoramic images the greatest deviation could be seen in the anterior area and in the paraxial images in the posterior area of the dental arch. For the patients about 67% of the tooth axes could be measured easily whereas the determination of the tooth axes was insufficient in 33% of the measured teeth.
Conclusion: Overall, the Dental CT is most suitable to find the topographical location of misplaced and impacted teeth. The angulation correction program, especially developed for this application, guarantees an exact metric analysis of tooth angulation independent of the patient's position in the CT. Dental CT and the angulation correction program form an optimal diagnostic instrument for presurgical planning and for orthodontic procedures, especially in cases having misplaced teeth.
Schlagwörter: dental, CT, tooth angulation, dental-CT, computer correction program
Poster 11, Sprache: Deutsch
The purpose of this study was to investigate the capability of 3rd year dental students without endodontic experience to start with ProFile .04 Taper (DeTrey Maillefer, CH).
To standardize the experimental design 102 industrial plastic blocks (Maillefer) were filmed before treatment. In total twenty-six subjects participated in the study: 12 dental students (DS) of the third year without any endodontic experience and 12 practitioners (P) with dental skill of one to ten years did 3 plastic blocks each. Furthermore a skilled endodontist (E) and a previously trained student (TS) operated another 15 each. For canal preparation up to #35 the manufacturers guidelines were followed, the canal was lubricated with glycerine and rinsed with water after each size. At the end every block was filmed again and the pictures were superimposed. The canal aberration was measured in 9 levels beginning at the apex. In total 16 instruments fractured: 1x#20, 2x#25, 10x#30 and 3x#35 thus being a rate of 9,41% (16 out of 170 instruments). Mean time for root canal treatment steadily decreased from the first block to the third in each group (DS: from 17,1 to 11,5 and 8,6 minutes; P: 10,2 - 6,5 - 6,3; E: 5,4 - 5,3 - 5,0; TS: 6,2 - 6,1 - 5,3) with dental students showing the highest speed up. All preparations exhibited a good taper, smooth walls and a definite apical stop. The most intensive work on the outer aspect of the canal was carried out near the apex (levels 1-3) for all groups with an aberration of 0,11 to 0,24 mm (DS), 0,18 to 0,19 mm (P) or 0,20 to 0,16 mm (E and TS). Regarding the inner aspect the removal increased steadily in all groups from level 1 to 6 and decreased slightly up to level 9. These findings show that even students lacking any endodontic experience can easily learn to use ProFile .04 with success and achieve a good root canal geometry.
Schlagwörter: NiTi, dental education, plastic block, ProFile, canal aberration
Poster 12, Sprache: Englisch
Loss of supporting zones during deciduous dentition effects the condylar growth and the spongybone density of the mandibular condyle. This is a quantitativeanalysis. The deciduous molars of micropigs are removed unilaterally. Sequence fluorochrome labeling is performed during the four month course of experiment.The examination is done on non-decalcified serial sagittal sections of the TMJ. The condyles of the distracted joints show a higher growth-rate compared to theextraction-side condyles, resulting in an 1.56 (p=0.003) times thicker additional vertical bone layer. This factor is ventral higher than dorsal (p=0.0311), increasing at the most from dorsomedial (1.33) to ventrolateral (2.38), which implies a reciprocal change of the condylar surface curve. However, the higher condylar growth of the unloaded condyles is correlated to a lower density of the corresponding subchondral spongy bone (7.38% difference, p=0.002). The total amount of bone produced is 1.33 times higher on the unloaded side. Aside with adaptive changes degenerative changes occur as well. So, for the first time the influence of unilateral loss of occlusal support on the mandibular condyles vertical growth, its trabecular bone volume and its amount of mineralized bone-matrix generated is quantified. Unilateral loss of occlusal support during deciduous dentition may lead to undesired adaptive and degenerative changes of the TMJ.
Schlagwörter: occlusal-support, unilateral-loss, quantification, condylar-growth, condylar-shape, subchondral-spongy-bone-density, degenerative-changes
Poster 13, Sprache: Deutsch
The objective of this study was the registration of incidence and etiology of alveolar process fractures in combination with other maxillofacial or dental fractures. The investigation demonstrated that the prognosis depends on the kind of management as well as the volume of concomitant injury. In a retrospective study over a period from 1995 to 1997 we examine 75 patients of the department of maxillofacial surgery of the Technical University of Dresden with upper and lower jaw alveolar fractures. Amongst the craniofacial fractures the maxillary alveolar fractures are with the incidence of 10 per cent of all craniofacial fractures more than twice as alveolar fractures of the mandible with 4 per cent. In the most cases the alveolar fractures were associated with various fractures of middle face and mandible. Additional, the fractures of alveolar process occurred very often in combination with dental lesions, for example with dislocation (26%), root fractures (13%) and crown fractures (8%). The frontal teeth of the upper jaw were mostly affected in both dentitions phases. Traffic accident followed by violence mainly caused the traumatic injury. In 90% of all cases the reposition of the fractures took place at the same day of injury. Isolated alveolar fractures were mostly treated by a plastic brace, which corporate covered the teeth. In case of combined fractures tabular brace were preferably applied. The miniaturization of the osteosynthesis material enables an increased the functional stable fixation of fracture fragment. Especially important is an immediate careful, if necessary, open repositioning and fixation with braces around the teeth. The three weeks immobilization time follows the common principles of fracture treatment. The best prognosis for the affected teeth of jaw segment is given, if no additional dental trauma occurred. Complications were in the most cases a result of additional affection of periodontium.
Schlagwörter: Alveolarfortsatzfraktur, Mittelgesichtsschädelfraktur, Unterkieferfraktur, Zahnfraktur
Poster 14, Sprache: Deutsch
The most frequent cause is the instrumentation beyond the apex with overfilling of rootfillmaterial in the canalis mandibulae. Chemical as well as mechanical factors have to be taken into consideration. An early surgical revision appears reasonable. The two presented cases show the necessary diagnostic and therapeutical procedure under special consideration of the forensic sequelae.
Schlagwörter: apical periodontitis, endodontic treatment, mental nerve, anesthesia
Poster 15, Sprache: Englisch
Although sports mouthguards provide protection against trauma, dentoalveolar injuries can still occur with the mouthguard in place. This study examined the effect of mouthguard protection in an in vitro model. A simulated maxilla, out of a PMMA arch containing replaceable resin teeth (Frasaco, Tettnang, Germany) was used to assess the performance of different mouthguard designs. 'Boil and bite' and custom-fitted mouthguards [ethylene vinyl acetate (EVA)] laminated with hard [polyvinylchloride (PVC)] or soft labial intermediate EVA layers were fabricated according to manufacturers' instructions. A steel ram was dropped onto the mouthguards at the maxillary incisor (21) region from a height of 25 cm (184 N i. e. fracture toughness of the resin tooth). The mV-peaks transmitted through the sample were measured at the back of the upper incisor (21) with a strain gauge. Ten readings were noted for each type of mouthguard. Data were analyzed by ANOVA at a significance level of 0.05. Bilaminated mouthguards with hard intermediate PVC layers of 0.8 mm, 1.5 mm or 2 mm thickness showed no significant differences to those of 1.5 mm thick soft intermediate EVA layers (peaks: -0.380 to -0.403 mV). Absorption rate amounted to 33 % compared with the unprotected tooth. 'Boil and bite' and mouthguards layered with silicon or with small hard PVC layers of 1.5 mm thickness demonstrated less absorption (peaks: -0.445 to -0.9 mV) and differed significantly from the other mouthguard systems (p < 0.05). These in vitro tests demonstrated that mouthguards laminated with soft EVA (1.5 mm thickness) or hard labial PVC (0.8, 1.5 or 2 mm thickness) intermediate layers protected artifical teeth more than those with small hard PVC intermediate layers or with silicon layers.
Schlagwörter: mouthguard, protection, trauma, absorption
Poster 16, Sprache: Englisch
The purpose of this study was to evaluate the marginal adaptation of two approximal ceramic insert systems before and after cementation to the cavities opened with ultrasonic tips. Proximal cavities with margins in enamel were prepared in a total of 40 intact molars using ultrasonic tips [SONICSYS approx tips (micro torpedo size #2 and #3, KaVo, Germany); Siplus Instrument approximal (U-shaped, Komet, Germany)]. The inserts of the similar sizes (n = 10) from two systems corresponding to the ultrasonic tips were placed in the cavities (SONICSYS Inlay, Vivadent, Germany; SDS-Inlay system, Schumacher Dental Systems, Germany), one on the mesial, the other on the distal side of the same molar. Marginal gap was measured before cementation. Following cementation (Tetric Flow, Vivadent, Germany) and thermocycling (5000 cycles, between 5-55*C) marginal quality was evaluated at the buccal and lingual walls, and pulpal floors of the proximal boxes under light microscope (x 150). ANOVA was used to analyze the data. The mean marginal gap of 25 µm (6 to 88 µm) recorded for SONICSYS inserts size #3 was not significantly different from that of SDS inserts of similar size [24 µm (6 to 78 µm)]. There was not a significant difference in marginal gap values between SONICSYS size #4 inserts (22 µm, 6 to 72 µm) and SDS inserts of similar size (34 µm, 6 to 104 µm) (p > 0.05). After cementation and thermocycling, five marginal discrepancies (less than 50 µm) for SONICSYS inserts size #3 and one for SDS size #2 inserts were found. One marginal microcrack for SDS inserts size #3 and four for SONICSYS size #4 inserts were observed. Comparison of mean gap values between the ceramic insert systems examined, revealed that marginal adaptation was better at the buccal and lingual proximal walls at both sizes from both systems than those at pulpal floors. Ceramic inserts placed in the cavities prepared with ultrasonic tips provide clinically acceptable marginal quality.
Schlagwörter: ultrasonic tips, ceramic inserts, marginal adaptation, proximal cavities
Poster 17, Sprache: Englisch
Minimal cavity preparation could be achieved with the use of ultrasonic tips. The purpose of this study was to evaluate the required time for opening the proximal cavities using three ultrasonic tips of different sizes and fine diamond burs (inlay burs, Intensive, Switzerland)/ultrasonic tip combinations. Proximal cavities with margins in enamel were prepared in a total of 40 intact molars using ultrasonic tips (SONICSYS approx tips micro torpedo, size #2 and #3, KaVo, Germany; Siplus Instrument approximal U-shaped, Komet, Germany and Piezon Cavity system 408, U-shaped, Electro Medical Sytems, Germany). The same procedure was repeated in another set of 40 molars which were prepared with fine diamond burs and finished with ultrasonic tips. ANOVA was used to analyze the data. The mean time required for opening small cavities recorded with Siplus (15 min, 13 to 17 min) was significantly longer than with diamond bur/Siplus tip combination (5 min, 4 to 6 min). Opening the cavities with only SONICSYS tips size #3 took 17 min (15 to 21 min) and size #4 19 min (16 to 22 min), which were also significantly longer than with diamond bur/SONICSYS tip size #3 combination (5 min, 4 to 8 min), and size #4 (8 min, 7 to 9 min). The mean time for opening the cavities recorded for Siplus tips of different sizes did not differ from the corresponding sizes of the SONICSYS tips (p > 0.05). Piezon cavity system required the least time both with tips (10 min, 8 to 14), and tips in combination with diamond burs (4 min, 3 to 5). Times required for proximal cavity preparation with ultrasonic tips were found to be longer than those with fine diamond bur/ultrasonic tip combinations. Proximal cavities opened with fine diamond burs and finished with ultrasonic tips provide short chairside times which are similar to conventional preparations.
Schlagwörter: ultrasonic tips, proximal cavities, required time, diamond burs
Poster 18, Sprache: Deutsch
In vitro and in vivo studies demonstrated that telescopic crowns with an occlusal (0.3mm) and lateral clearance (0.03mm) between inner and outer part have potential as overdenture abutments specially in cases of severely mutilated dental arches. The aim of the study was to evaluate the influence of the plaque-accumulation (PI) at the margins of the copings for two different designs of telescopic crowns (CC, C0) and bases of the prostheses (LVC, LV0) on the plaque stream into the periodontal pocket (PP). Two identical models simulating a lower jaw with 3 prepared teeth served as in-vitro samples. The finishing lines of the cylindrical preparations were made with a chamfer at the gingival level (CC) on one model, in contrast to no chamfer (C0) on the second. Natural plaque cultivated on agar plates was applied on the copings to obtain a plaque-index (PI) of 2-3 (Silness & Löe, 1964). Central load of the dentures was provided by a pneumatic piston of a fatigue loading device (F=50N, interval=1Hz) via a metal plate. In the regions of the interrupted buccal flange of the denture (lingual vault complete (LVC)) the transparent PMMA model allowed an observation of the plaque-distribution inside the periodontal pocket. The number of chewing cycles necessary for the plaque to reach the bottom of the simulated periodontal pocket with a depth of 2,4 or 6mm was recorded. This experiment was repeated after the denture vault was removed at the lingual region of the abutments (LV0). Statistical evaluation of the data was conducted using StatView 5.0 (ANOVA: a= 0.001; post hoc-test after Bonferroni/Dunn).
The results were:
The numbers of cycles for the plaque to reach the bottom of PP correlated significantly.
Schlagwörter: Resilienzteleskop, in vitro, Plaque, Prothesenbasisextension
Poster 19, Sprache: Deutsch
The coming through of wisdom teeth depends to a high degree on the dimension of the retromolar space as well as on the position of the third molar germs. The intention of this study was to investigate the reproducibility of various parameters to give an opinion concerning the retromolar space. For this reason on panoral radiographs and lateral cephalometric radiographs of 21 patients the size of the retromolar space, the angulation of the third molar germs to the occlusal plane and their vertical position were measured. Measurement was done twice by two examiners. Between the examiner results no systematic deviations were detected. The investigated parameters for judging the dimension of the retromolar space and the position of the third molar germs turned out to be sufficiently exact.
Schlagwörter: wisdom-teeth, retromolar-space, panoral-radiograph, lateral-cephalometric-radiograph