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Biomedical subjects

G J Ziebert

Publications and source records attributed to G J Ziebert.

At least 19 recordsLinked to original sources
PubMed1991

A comparison of impression materials for complete-arch fixed partial dentures.

This study compared the marginal fit of complete-arch fixed prostheses under simulated clinical conditions. Prostheses were made on casts constructed from three commonly used impression materials; polyether, polyvinyl siloxane (medium-viscosity and putty-wash), and reversible hydrocolloid. A maxillary dentoform with four abutment teeth was used as the master cast and six impressions were made with each material. Individual castings for each abutment were made on the stone casts. The abutment castings were luted together on the casts to provide a complete-arch fixed partial denture using a ticonium framework and acrylic resin. The marginal fit of the abutment castings was measured on the master cast before and after the prostheses were luted together. The polyether and both addition silicone impression materials were significantly more accurate than the reversible hydrocolloid in both situations. All of the single castings were clinically acceptable, but the luted restorations made from reversible hydrocolloids were not.

Analysis of Variance↗
PubMed1991

Observations on the motor control of brief teeth clenching in man.

Without artificial feedback control, maximum voluntary isometric contractions were performed for about 1 s by six subjects. Randomly selected surface electromyograms of the anterior temporalis and masseter muscles suggested that, in some cases, the motor control of the entire isometric contraction might have been preprogrammed through the phenomenon of anticipation. In the majority of cases, the control of the initial contraction phase might have been preprogrammed, followed by a phase of servo-controlled motor activity. As a functional basis for the servo-control of isometric force generation, it was suggested that compartmentalized 'extrafusal and intrafusal motor units' were recruited and decruited in an orderly manner, and periods of alpha-motor inhibition were interpreted as signs of switching from one control scheme to another, possibly via a transcortical loop.

Adult↗
PubMed1991

An electrognathographic study of aspects of 'deprogramming' of human jaw muscles.

Three-dimensional electrognathography of an incisor point was used to detect peripheral correlates of deprogramming of the jaw elevator muscles. Putative deprogramming was attempted through the clinically recommended use of a leaf gauge, placed for 10-15 min between the maxillary and mandibular anterior teeth and disoccluding the posterior teeth by about 2 mm. Studied mandibular displacements were those that occurred during voluntary elevation of the mandible from the postural to the intercuspal position. Use of the leaf gauge did not affect the displacement patterns. Within a freeway space of about 0.2 mm3, the incisor point moved about 2 mm vertically, about 1 mm sagittally, and about 0.2 mm laterally.

Adult↗
PubMed1991

Postural contractile activities of human jaw muscles following use of an occlusal splint.

As induced by an occlusal splint over a period of 1 week, this study monitored surface electromyographic changes in the postural contractile activities of jaw elevator and depressor muscles in six healthy adults. The immediate effect of the occlusal splint was to increase the postural contractile activities of the suprahyoid muscles. All postural muscle activities showed wide-ranging biological variation, but the activities induced by the splint tended to stabilize within 1 week, with decreased postural activities in the masseter and anterior temporalis muscles, and increased postural activities in the suprahyoid muscles.

Adult↗
PubMed1990

An electromyographic study of aspects of 'deprogramming' of human jaw muscles.

Surface electromyograms from the right and left masseter and anterior temporalis muscles were used to detect peripheral correlates of deprogramming, also known as programming and reprogramming, of jaw elevator muscles. Putative deprogramming was attempted through the clinically recommended use of a leaf gauge, placed for 15 min between the maxillary and mandibular anterior teeth and disoccluding the posterior teeth by about 2 mm. Studied contractile activities were those of postural activity (subconscious, semi-isometric, minimal activity) and intercuspal teeth clenching (conscious, isometric, maximal activity). Use of the leaf gauge did not affect normalized postural activity (about 4%), the duration (about 900 ms) and static work efforts of clenching (about 1200 microV.s), the time to peak mean voltage of clenching (about 400 ms), and the peak mean voltage of clenching (about 300 microV). Activity and asymmetry indices showed that the studied motor innervation patterns were not changed by the leaf gauge.

Adult↗
PubMed1988

Accuracy of impression materials for complete-arch fixed partial dentures.

The accuracy of 12 impression materials of six different types were studied by using complete-arch FPD impressions. Sixty impressions were made of a Columbia dentoform maxillary model with complete cast crown abutment preparations on the canines and the second molars. A one-piece casting was constructed by connecting the four individual castings made for the four abutment teeth. The master prosthesis was seated on the stone casts produced from the impressions. The marginal adaptation on the four abutments was then evaluated with a travelling microscope. The individual marginal adaptation of the four castings on the abutments was also examined after sectioning the four joints. The following conclusions were drawn. 1. The polyethers produced the most accurate complete-arch replicas. The second most accurate were the vinyl polysiloxanes, followed by the polysulfides and the irreversible-reversible hydrocolloids. The least accurate were the reversible hydrocolloids and the irreversible hydrocolloids. 2. The polyether impression materials exhibited the most consistent accuracy for a master cast to fabricate a complete-arch FPD.

Alginates↗
PubMed1988

Accuracy and comparative stability of three removable die systems.

A study was performed to evaluate three removable die systems: the Accu-Trac, the Pindex, and the conventional brass dowel pin technique. The stability of the dies in the mesiodistal, bucco-lingual, and gingivoocclusal directions was compared. Under the conditions of this investigation, the following conclusions were drawn. 1. No significant difference was found in the shift of the removable die in a horizontal direction between any of the three systems. 2. No significant difference was found in the displacement of the removable die in the vertical direction with the Pindex system and the conventional dowel pin techniques. The slight displacement that did occur was in an upward direction. 3. A significant vertical displacement of the removable die in a downward direction was found with the Accu-Trac system compared with the other two systems.

Denture Design↗
PubMed1986

Accuracy of one-piece castings, preceramic and postceramic soldering.

An investigation was conducted to evaluate the relative accuracy of one-piece castings of FPDs of three, four, and five units with those assembled by preceramic soldering and postceramic soldering. The preceramic soldered FPDs were subjected to six simulated porcelain firing cycles to assure a homogeneous sample. A total of 15 FPDs, five of each length, were evaluated for each test condition. A three-piece aluminum mold with stainless steel dies, which allowed for varying the length of the prosthesis, was used to fabricate the FPDs in 52% gold-palladium alloy. Marginal discrepancies of the castings on the dies were compared for the three test techniques. The mesiodistal length of the FPDs that were pre- and postsoldered were also measured at the occlusal and at the gingival margins and compared with the restorations before soldering.

Dental Casting Technique↗
PubMed1986

Effects of experimental loss of teeth on the temporomandibular joint.

A review is presented of the effects of loss of teeth, with impaired occlusal stabilization, on the temporomandibular joint in experimental animals. Loss of teeth, with subsequent abnormal loading of the temporomandibular joint, leads to histomorphological, pathological and pathophysiological changes in the articular cartilages, the articular disc, the synovium, and the bony articular components. The severity of the changes increases with increasing age, and an existing arthritis of the joint is aggravated by impaired occlusal stabilization. The experimentally induced changes resemble those in human subjects with extensive loss or extensive attrition of teeth.

Animals↗
PubMed1985

Comparison of accuracy of multiunit one-piece castings.

An investigation was conducted to evaluate the accuracy of one-piece castings of FPDs consisting of three, four, and five units with a ceramometal alloy cast in a large circular ring. A three-piece aluminum mold with stainless steel dies simulating the various lengths of the FPDs was used. A total of 18 castings, six castings for each FPD, were fabricated. Marginal discrepancies of the castings on the dies and the length of the castings were compared before and after sectioning the castings at the connectors. The following conclusions were drawn from the study. Seating of the castings improved approximately 50% after sectioning, which indicates that the castings were distorted. The distortion was a three-dimensional phenomenon, with the greatest discrepancy on the mesiogingival surface of the anterior retainer and on the distolingual surface of the posterior retainer. The distortion was least for the three-unit FPDs and greatest for the five-unit FPDs. The lingual-facial diameter of the castings at the gingival axial line angle was significantly larger than the dies in most cases. The mesiodistal diameter of the castings at the gingival axial line angle was smaller than that of the dies but was only significant with the three-unit FPDs. Although the castings were slightly oversized or undersized, the primary reason the castings did not seat was warpage.

Dental Alloys↗
PubMed1984

Stabilized baseplate technique for interocclusal records.

A technique that provides a stabilized baseplate to facilitate jaw registrations in partially edentulous arches with prepared teeth has been described. The technique provides for accurately recording maxillomandibular relations when there are few teeth and interarch stabilization is difficult to achieve.

Acrylic Resins↗
PubMed1979

Tooth contacts and stability before and after occlusal adjustment.

A study was undertaken to analyze the possible relationship between the number and type of tooth contacts before, immediately after and 16 weeks after occlusal adjustment and their influence upon occlusal stability. The data collected from 10 adult subjects who required an occlusal adjustment indicated the following: 1. Six of the ten subjects had no clinically perceptible "slide from centric relation" 6 weeks after occlusal adjustment, and the number of teeth and number of contacts were virtually the same immediately after 6 weeks after occlusal adjustment. 2. The remaining four subjects, whose occlusions had relapsed after adjustment, had one dental arch that included a missing tooth. It would seem that dental arches interrupted with extraction spaces do not remain stable with occlusal adjustment alone. 3. The type of tooth contacts that are the most stable are those of a cup against a flat plane (e.g., bottom of a fossa or marginal ridge) or those of a combination of a cup against a flat plane and one or more inclined planes.

Adult↗