Complete denture displacement following open-mouth reline.

In 21 complete denture wearers, six upper and 15 lower denture relines were performed with the open-mouth technique. The centric relation (CR) was recorded with the Central-Bearing-Point (CBP) method three times before and three times after the reline. For each registration, the right and left condylar position was recorded in three dimensions using a custom-made measuring device. The average denture displacement from an initial reference position (CR) was calculated for each registration. An upper denture reline leads to a mean displacement of 2·5 mm, both in the right and left condylar area. With an average of 2·0 mm, this displacement was smaller following a lower denture reline (right and left mean, 1·6 mm). The precision of the CBP-registrations proved 0·5 mm before and 0·3 mm after reline; hence, the measured condylar displacement after reline could not attribute to a methodological bias. This clinical-experimental study demonstrates that relining complete dentures with the open-mouth technique may lead to a substantial denture shift and thus imply inevitably clinically relevant occlusal discrepancies. It is therefore important to carefully check the occlusion at denture delivery and remount the prostheses if necessary.

[Development of a periodontium-approximated specimen holder for attrition studies of telescopic crowns]. / Entwicklung eines parodontienadäquaten Probenhalters für Verschleissuntersuchungen von Teleskopkronen.

To enable attritional studies on telescopic crowns, a specimen holder has been constructed that is intended to simulate, in zero approximation, the biomechanical properties of abutments bearing telescopic crowns. The specimen holder consists essentially of a system with two metal "concertinas" with different elasticity constants reflecting the different biomechanical parameters for periodontium and bone. The biomechanical processes in the periodontium are too complex to be simulated accurately in vitro. Nevertheless, the specimen holder described here enables the forces acting during insertion and removal of a partial denture to be accommodated elastically in the angular and axial directions, to simulate the possible degrees of freedom of the abutments in situ. In this way, the unavoidable errors of specimen fixation are rendered tolerable, so that local preferential wear is decisively reduced.

[Design and testing of a novel measuring system for use in dental biomechanics--principles and examples of measurements with the hexapod measuring system]. / Aufbau und Erprobung eines neuartigen Messsystems für die dentale Biomechanik--Messprinzip und Beispielmessungen des Hexapod-Mess-Systems.

A novel measuring set-up based on a hexapod system for use in dental biomechanics is described. It was specially developed to measure force/deflection characteristics of different dental materials and devices. The functionability and suitability of the system for use in experimental biomechanics were investigated in two different studies. In a first study the micro mobility of prosthetic telescopic crowns prior to and after simulated wear was determined to investigate the influence of wear processes on the stability of the anchorage elements and thus of prostheses. This study investigated the ability of the setup to load a specimen with high forces or torques of up to 100 Newton. The second study looked at the force/deflection characteristics of orthodontic anchorage pins used in orthodontics to additionally stabilize the anchorage unit, for example during molar movement. In this study specimens were loaded with small forces of less than 10 Newton, as are typically used in orthodontics. Using the setup, the deflection behaviour of these devices under high and low loading was measured at a resolution of approximately one micrometer or one angular second.

[The distance between the terminal hinge position and the intercuspation position in the temporomandibular joint area]. / Distanz zwischen terminaler Scharnierachsenposition und Interkuspidationsposition im Kiefergelenkbereich.

In 117 subjects with normal TMJs, the distance between most retruded contact position and maximum intercuspation was measured both extraorally by means of a kinematic face bow and intraorally with a ruler. The mean distance between most retruded contact position and maximum intercuspation was 0.5 +/- 0.3 mm on the right side and 0.5 +/- 0.4 mm on the left side. The reproducibility of the measurements was better than 0.3 mm (0.2 +/- 0.1 mm) in 80% of the subjects. Statistically, there was no correlation between the amount of sliding and vertical overlap. For practical purposes, the following conclusions can be drawn: 1. Retruded contact position and maximum intercuspation are well reproducible reference positions of the mandible. 2. Retruded contact position is very close to maximum intercuspation in most people. Therefore it can be used as a "therapeutic compromise" for occlusal rehabilitation. 3. There is no indication that a deep vertical overlap would lock the mandible in a dorsal position. 4. When using the "freedom in centric" concept, the occlusal range is about 0.5 mm.

[The intraoral determination of the sagittal condyle path inclination during face-bow recording]. / Intraorale Bestimmung der sagittalen Kondylenbahnneigung während der Gesichtsbogenübertragung.

In a clinical trial involving 40 fully dentate persons, three different intraoral procedures to determine the sagittal condyle path inclination were checked for accuracy. In each test person the condyle path inclination was determined three times, i.e. by the central bearing point method, the protrusive check-bite method and by a protrusive bite record integrated in the bite fork. At 5 mm of protrusion the reproducibility of the results obtained with the central bearing point method (mean value 2.1 +/- 2.0 degrees) were far better than that with either of the two other methods; the difference was statistically significant. The protrusive check-bite records and the protrusive bite fork records did not differ from each other as far as their accuracy was concerned (mean values 3.6 +/- 2.1 degrees and 3.4 +/- 1.6 degrees, respectively). The mean value of the condyle path inclination to the hinge axis infra-orbital plane in the sample was about 50 +/- 8 degrees regardless of the method used. Thus, protrusion records can be integrated in the face bow transfer.

[Variation of the terminal hinge axial position in different methods of registration]. / Variation der terminalen Scharnierachsenposition bei verschiedenen Registriermethoden.

In order to determine the variation of individual terminal hinge axis positions in the sagittal plane, 118 stomatognathicly healthy patients were subjected to three occlusal registration methods. The Lauritzen manipulation method, the Dawson registration method and the McGrane central bearing point method were carried out on each subject. The paraocclusal pneumatic axiography was used for direct measurements on the subjects. The mean values obtained for the Lauritzen terminal hinge axis position differed from those of the Dawson position by about 0.2 +/- 0.2 mm on the right side and by about 0.3 +/- 0.2 mm on the left. 68% of the Dawson registrations were positioned cranially to the Laurizen axis location. The position determined by means of the central bearing point method differed from the Lauritzen position by 0.4 +/- 0.3 mm on the right and by 0.4 +/- 0.2 mm on the left. 64% of all registrations were positioned cranially in relation to the Lauritzen reference points. It is concluded that different methods of terminal hinge axis recording show slight variations in position of the individual terminal hinge axis location, i.e. mandibular position.

[The reproducibility of arrow-point registration in full-dentition subjects depending on the recording material]. / Reproduzierbarkeit der Pfeilwinkelregistrierung bei Vollbezahnten in Abhängigkeit vom Registratmaterial.

The reproducibility of the intraoral central bearing point method was measured in 46 dentate subjects with a healthy stomatognathic system. Nine complete registrations were carried out on each volunteer, while three different materials were used for fixing the upper to the lower jaw. The occlusal records were examined in the condylar area on a specially designed articulator. Two therapists took part in this study. The shifts of the condylar spheres in all three spatial directions were found as follows: Ramitec 0.14 +/- 0.16 mm, Super-Bite 0.15 +/- 0.14 mm and Bite Compound 0.15 +/- 0.16 mm. The movements of the condylar spheres in space were calculated. They amounted to 0.28 +/- 0.23 mm when using Ramitec, 0.28 +/- 0.20 mm when using Super Bite and 0.31 +/- 0.23 mm when using Bite Compound. Statistically, the differences between the data of the three materials were not significant. Also, the results of our random sample were independent of the therapist.

[The reproducibility of the abutment angle recording in the remounting of complete dentures]. / Reproduzierbarkeit der Pfeilwinkelregistrierung bei der Remontage von Total-Prothesen.

Upon insertion, 40 newly made full dentures could be remounted three times in succession by each of two therapists by means of the intraoral central bearing point method. The records were measured electronically and by computer in a special measuring articulator in the right and left condylar area. The shift of the condylar spheres in the three different records was smaller than about 0.3 +/- 0.2 mm in all three spatial directions. From this we calculated the movement of the spheres in space to be about 0.5 +/- 0.3 mm. The results of our random samples were independent of the therapist, the patients' age or sex, the period for which the patients had been edentulous, the sliding of the dental prostheses on the tegmentum or the anatomical shape of the alveolar ridges.

[The reproducibility of the manual checkbite in the wearers of complete dentures]. / Reproduzierbarkeit der Handbissnahme bei Totalprothesenträgern.

Thirty-six new complete dentures were remounted by means of check bite records at the time of placement. The mandibular position was recorded three times in each patient by two clinicians using Bite Compound, a thermoplastic material, for the records. After individual transverse horizontal axis localization, the dentures were mounted in an articulator, and subsequently three-dimensional, electronic and computerized measurements were made with a special measuring instrument. In intraindividual comparison the reproducibility of the check bite records resulted in a mean value of 0.37 +/- 0.33 mm, whereby maximum deviations of up to 1.8 mm were observed. Repeated insertion of the maxillary dentures into the hardened impressions of the thermoplastic compound led to an error of 0.04 +/- 0.06 mm. The results of the two clinicians differed only slightly.

The lateral leeway in the habitual intercuspation: experimental studies and literature review.

The habitual intercuspation is used ubiquitous for manufacturing small dental restorations. However, a little is known on its precision. The aim of the present study was therefore to investigate the unambiguity and accuracy of the habitual occlusion in mounted plaster casts from fully dentate persons. Eighty-one fully dentate volunteers, 36 women and 45 men aged 26.8 +/- 6.2 years (18-55 years), with minor fillings and no signs or symptoms of TMD took part in the experiments. Silicone impressions were taken, poured with stone plaster and the obtained casts mounted into Dentatus ARL(R)- articulators using an individual face bow transfer. Subsequently, the models were transferred to a custom-made measuring articulator where the lateral leeway and the accuracy of the hand-held habitual intercuspation were quantified in the condylar area. Measurements were repeated seven times with the upper cast pushed either to the maximum right or the maximum left intercuspation. The hand-held habitual intercuspation of upper and lower cast proved ambiguous in 57% of pairs of casts. The average lateral leeway of the habitual intercuspation in the condylar area was 0.10 +/- 0.05 mm (0-0.51 mm; median 0.07 mm) between the maximum right and left occlusal positions. The average accuracy of three repeated measurements was 0.22 +/- 0.09 mm (0.02-1.17 mm; median 0.16 mm). Natural occlusal surfaces in a full dentition do not guarantee an unambiguous habitual intercuspation of the plaster casts. The described leeway and technical limits might be possible causes for occlusal adjustments that are sometimes necessary when inserting restorations manufactured in habitual intercuspation.

Studies of changes in occlusion after the insertion of complete dentures (part II).

The aim of this clinical experimental study was to investigate whether, and what, changes in occlusion occur between 3 weeks and 1 year after insertion of complete dentures. Twenty-six edentulous patients, who already had their jaw relation registered for part I of this study some 357 days before, were re-examined. The same special non-arcon measuring articulator was used for determination of any positional differences between the presently recorded central condylar position with inter-occlusal gap and the equilibrated intercuspal position, from approximately 1 year previous. Differences were recorded electronically in the condylar area in three dimensions. The position of the condylar balls of the measuring articulator in maximum intercuspation had shifted, since the previous recording, by about 0.62 +/- 0.04 mm (0.04-1.76 mm) in the sagittal and 0.89 +/- 0.72 mm (0.01-3.06 mm) in the vertical direction. Whereas the differences measured in maximum intercuspation scattered in the sagittal plane uniformly around the centric condylar position, in the vertical plane they were shifted cranially about an average of 0.77 +/- 0.85 mm (1.06 mm caudally to 3.06 mm cranially). The results indicate that in half of the patients from the present sample the occlusion did not remain stable, which is assumed to be mainly caused by resorption of alveolar bone and abrasion of the acrylic teeth. Therefore, at each check-up visit not only the health of the denture-bearing tissues and the fit of the dentures, but also the mandibular posture and the occlusion should be examined carefully.

Studies of changes in occlusion after the insertion of complete dentures. Part I.

The present study aims to investigate changes in the occlusion of complete dentures after their insertion. A total of 85 edentulous patients were provided with new complete dentures. Their individual hinge axes were determined using mechanical axiography and the upper finished dentures were transferred by facebows to Dentatus articulators. The lower dentures were mounted according to an intraoral central bearing point (CBP) registration and equilibrated in terminal hinge position. An articulator specially modified for measurements in the condylar area was used. The differences between the positions of the condylar balls with CBP registration and those after equilibrating the occlusion were determined. On average, 19 days after insertion, 71 patients took part in a follow-up examination. As in the first session, the terminal hinge position was registered with the CBP method using the apex of the Gothic arch. Thus, the positions of the condylar balls immediately after the new registration could be compared with those in equilibrated intercuspation 3 weeks earlier. The differences were found to be 0.5 +/- 0.4 mm (0-2.9 mm) in the three axes (sagittal, coronal and horizontal). They are thought to result from settling into the denture bearing tissues and also from neuromuscular adjustment of the masticatory system. Compulsory remounting of complete dentures after insertion is therefore recommended.

[Problems of mandibular position diagnosis using paraocclusal mechanicpneumatic axiography]. / Zur Problematik der Positionsdiagnostik mit Hilfe der Achsiographie.

Based on mechanical axiographic examinations of 117 test persons with normal masticatory functions, the reproducibility of the recordings was assessed at 0.2 mm +/- 0.14 mm with maximum deviations of about 0.8 mm. The reproducibility of the protrusion tracings was 7 degrees +/- 7 degrees at 1 mm of protrusion (maximum: 37 degrees) and 2 degrees +/- 2 degrees at 5 mm of protrusion (maximum: 11 degrees). The diagnostic assessment of the positions of the mandible is complicated by the fact that asymmetrical deviations on the right and left may result in errors in the interpretation of distances and directions of deviation.

[Cervical discrepancies and closeness of marginal fit of full cast crowns in correlation with the luting agent used]. / Zervikale Diskrepanzen und Randschlussdichte von Vollgusskronen in Abhängigkeit vom Befestigungszement.

In an in-vitro study 75 extracted teeth were prepared with a chamfer and a 12 degree convergence angle. After corrective impression taking and preparation of the dies accurately fitting caps were made of "Stabilor G" alloy. The marginal defects were measured at 4 points on each tooth under the light-microscope before and after cementing with three different luting agents. Before cementation the mean values and standard deviation of the cervical discrepancies were 105 +/- 43 microns. The crowns fixed by means of zinc oxyphosphate cement (Harvard) exhibited marginal defects of 142 +/- 33 microns, those fixed with Fuji-Ionomer type I glass polyalkenoate cement had 159 +/- 20 microns, and the crowns cemented with Ketac-Cem had 127 +/- 6 microns. After exposing the specimens to thermal cycling, additional data on the sealing capacity of these cements could be obtained which showed zinc oxyphosphate cement to have the most favorable properties.

[Adhesive strengths of cast crowns with various types of cements]. / Haftkraft von Vollgusskronen in Abhängigkeit vom Befestigungszement.

In an in vitro study the adhesive strength of sand-blasted castings (gold alloy) was tested on human teeth prepared and finished in different ways. For cementation we used two glass ionomer and one phosphate cement. On the surfaces treated with carbide finishing instruments the force required for separating the crown from the tooth was about 1.9 N/mm2 for Ketac-cem, about 2 N/mm2 for Fuji Ionomer, and about 1.8 N/mm2 for Harvard (a zinc oxide phosphate cement). Compared with this, the values obtained for dentin surfaces pretreated with fine diamonds (red ring) were 1.5 N/mm2 for Ketac-cem, 1.6 N/mm2 for Fuji Ionomer, and 1.9 N/mm2 for Harvard. The measured differences between the various types of cement were statistically not significant.

Studies on adaptation to complete dentures. Part II: Oral stereognosis and tactile sensibility.

High oral perception is thought to contribute to poor adaptation to new dentures. The aim of this study was to evaluate the oral stereognosis and tactile sensibility in edentate subjects and relate these to patient age and capability of adaptation to new prostheses. A total of 67 patients were provided with new complete dentures 2-3 weeks before the experiment. In 54 subjects, the oral stereognosis was evaluated by 12 different test-pieces, which were placed unseen on the tongue and had to be recognized. In 38 patients, the oral tactile sensibility was determined in the premolar area using copper foils. The capability of adaptation was evaluated by a questionnaire. Denture retention was assessed by clinical examination. The number of correctly identified test-pieces and the average identification time were related to the age, but no relation was found to patients' capability of adaptation. The tactile sensibility was found to be impaired with age and diminished capability of adaptation. Both adaptation and oral tactile sensibility were significantly lower in subjects with poor lower-denture retention. In conclusion, the results cannot support a relationship between high oral stereognosis and adaptation problems. However, good denture retention facilitates the adaptation process.

Accuracy of check-bite registration and centric condylar position.

In a dentate subject a jaw relation can either be determined in maximum intercuspation and is as such given by the occlusal morphology, or the mandibular position can be allocated according to the centric position of the condyles. For comprehensive restorative treatment or analytic measures of the occlusion it is important to record the centric condylar position. Various registration methods have been described in the literature, but there is no consensus on which is the 'best'. The aim of the present study was therefore to assess the accuracy of various registration methods and evaluate a possible influence of the used materials. Four dentists were involved in the clinical part of the study, another was responsible for the measurements. Impressions were taken from 81 fully dentate volunteers. The casts were mounted by face-bow transfer and central-bearing-point (CBP) registration into Dentatus articulators. Subsequently the centric condylar position was determined with six different methods and materials, respectively. Each method was reproduced twice so that a total of 18 registrations was performed per patient. The mandibular positions which resulted from the individual registrations were then repeatedly compared in the condylar area using a computer supported specially modified measuring articulator. The accuracy was found best for the unrefined wax wafer registration (x=0.33 mm) and with an average of 0.44 mm worst when using acrylic wafers. The CBP and frontal jig methods as well as tin-foil and refined wax wafers showed an accuracy in-between these boundaries. The biggest measured mandibular displacement between any two registrations were considerably 2.0 mm. However, the described differences in accuracy between the various methods and materials proved statistically not significant. All investigated jaw registrations showed an accuracy of about 20 times the tactile fine sensibility of natural teeth which has to be taken into account when inserting fixed prosthetic restorations in centric condylar position. Despite meticulous clinical and technical procedures small occlusal adjustments are therefore almost unavoidable.

Functional impression and jaw registration: a single session procedure for the construction of complete dentures.

The conventional fabrication of complete dentures involves two separate clinical sessions for functional impression making and jaw registration. The presented method combines both procedures in one session. The aim of this study was to survey the three-dimensional tooth positions in complete dentures with reference to the ridges to establish arbitrary guideline values that could be used for the manufacturing of tooth-position analogue plastic rims on functional impression trays. New complete dentures were fabricated by supervised undergraduate students in the conventional manner for 104 edentulous patients. The position of the maxillary teeth was surveyed in the horizontal plane using the Schmuth 'vizor-measuring plate'. The vertical dimension of occlusion, represented as the distance between opposing ridge areas of the dentures in maximum intercuspation, was measured at different sites by means of a Gutowski gauge. The tooth positions on the dentures varied widely, e.g. the horizontal distances between the incisive papilla and the maxillary incisors was 7.1 +/- 2.3 (3-14) mm. The vertical dimension of occlusion, which is most important in the jaw registration, varied equally with an anterior inter-alveolar distance between 12 and 33 (20.4 +/- 4.0) mm. Arbitrary moulding of the tooth position-analogue plastic rims does not seems to be an ideal method of pre-shaping functional impression trays, because the individual anatomical variation is considerable. Alternatively, the horizontal and vertical tooth positions of functionally and aesthetically pleasing dentures should be measured to pre-shape the rims of functional impression trays in the maxillary and the mandibular jaw. Such trays are a valuable tool for functional impressions and an immediate preliminary jaw registration in the fabrication of new complete dentures. This method allows a first try-in of the full set-up in the third clinical visit without loosing precision.