Jon Ørstavik

Retention of complete maxillary dentures related to soft tissue function.

The influence of free tongue, lip, and cheek function on the retention of complete maxillary dentures was investigated for five experienced denture wearers. Test dentures were designed with full palatal coverage and functionally determined filling in of the vestibular sulcus. The front teeth were arranged primarily to meet cosmetic demands--that is, anterior to the top of the residual alveolar ridge. Retention was measured as resistance to dislodgement-provoking loads applied vertically to the incisive edge of the central incisors, using a miniature bite force recorder. All the participants were able to load their front teeth with 35 N or more without loss of retention. None of them experienced denture dislodgement provided the tongue, lips, and cheeks wee allowed to act freely. If the peripheral soft tissues were separated from the vestibular denture flange, no obvious effect on denture retention could be detected. Physically preventing the tongue from pressing against the posterior part of the denture reduced the retention significantly. Measurements of anterior loads tolerated after stepwise reductions of the denture extension indicated that the tongue acted primarily by pressure against the tuber regions. Tongue pressure against the central parts of the palate and lip or cheek pressure against the vestibular flange seemed to be of less importance.

Retention of complete maxillary dentures as a result of changes in design

The influence of complete maxillary denture design on retention was studied under clinical conditions simulating chewing. Five persons with an edentulous maxilla and a natural dentition of at least 10 teeth in the mandible participated. Retention was measured with a miniature bite force sensor. The occlusal load required to provoke denture dislodgement was recorded. The general principles of denture design were as follows: the bicuspids and molars were set on top of the residual ridge; the thickness of the denture borders was determined functionally; and the palate was covered to the vibration line, without attempts at border compressions. The details that were changed to evaluate their influence on denture retention were as follows: the point of attack of the dislodgement-provoking load alternated between three distinct pits, situated 2 mm apart in the buccopalatal direction on the occlusal surface of the first right bicuspid; the vestibular denture border on the left side was reduced stepwise to 75%, 50%, and 25% of its original thickness; and the distal extension of the palatal denture border was shortened stepwise (2 + 2 mm, as measured in the midline). Measurements pertaining to one specific problem were carried out within a period of 2 h. The results confirmed the concepts that lingualized occlusal contact, functionally determined filling in of the vestibular sulcus, and full palatal coverage to the vibration line all have a positive influence on the retention of complete maxillary dentures.

Retention of complete maxillary dentures measured as resistance against unilateral occlusal loading

Complete maxillary dentures were tested for their ability to remain in place when subjected to unilateral occlusal loads. The test material comprised five persons, each supplied with three identical dentures. The denture design was based on the principles of 1) functionally determined filling-in of the vestibular sulcus, 2) palatal coverage to the vibration line without post dam, 3) aesthetically governed positioning of the front teeth, and 4) positioning of the lateral teeth in the plane connecting the top of the residual ridge with the central part of the occlusal surface of the antagonizing natural teeth. Resistance to unilateral occlusal loads was measured by means of a miniature bite force sensor. In the pooled material, an average load of 70 N was tolerated before the dentures were dislodged. For a given participant/denture combination, the resistance against dislodgment varied considerably when tested on different days. Marked differences were also found among three identical dentures in one person. The tolerance against unilateral occlusal loads could feasibly be quantified. However, the influence of specific clinical and/or technological factors on denture retention during function should be studied only if strict definitions as to the test conditions are given. These conditions must include the time, person, and denture tested.

Two-Hour Bacterial Colonization of Dental Luting Cements in Vivo

Test specimens of zinc phosphate, polycarboxylate, zinc oxide-EBA, silico-phosphate and resin cements were carried in the mouth for 2 hours. The bacteria adhering to the cement specimens were quantified after culture on selective and non-selective, solid media. Significantly fewer bacteria could be recovered from the EBA cement than from the other cement types. All cement specimens, as well as samples from tooth surfaces, showed selective enrichment of Actinomyces viscosus compared with the proportion of this organism in saliva. The silico-phosphate and particularly the polycarboxylate cement were poor substrates for the adhesion of Streptococcus mutans. Scanning electron micrographs revealed heavy accumulations of coccoid and filamentous organisms on zinc phosphate cement surfaces. Fewer bacteria, mainly cocci, were seen on the polycarboxylate and silico-phosphate cements, whereas the micrographs of the EBA and resin cement surfaces were difficult to interpret.

Copper-band impressions for complete crown abutments

I he adaptation of a complete crown to the gingival margin is an important factor for the sound prognosis of teeth. Ill-fitting margins contribute to the accumulation of bacterial plaque and thus predispose the tooth to caries and periodontal disease.’ Therefore, an exact reproduction of the abutment at the finishing line of the preparation is of particular importance among the several factors’ governing the proper seating of complete crowns. Since the impressions must also include a narrow zone of unprepared tooth hurface immediately apical to the finishing line, they are usually removed over more or less pronounced undercuts. Consequently, the impressions are highly liable to deformation in this critical area. This clinical problem has been greatly reduced in recent years by the introduction of the tray impression technique combined with highly elastic impression materials. However, individual impressions of each abutmc’tlt using relatively tight-fitting impression bands are still preferred in SOIII~ c,lirricnl instances. Both thermoplastic and elastic compounds are commonly used with this technique. A description of their physical properties will give a clue to the range of indication for each material, but little seems to have been done to stud) thfair suitability specifically for the copper-band technique. The present investigation studied the applicability of one thermoplastic material and different types of elastic materials for the copper-band technique. The impressiol t technique simulated the clinical method, often resorting to relatively tightfitting bands when the application ‘of impression material subgingivally is difficult. Impressions were taken of abutments with varying degrees of taper belobv the finish ing line. The impressions were inspected for rupture of the materials, and the exactIIC~\ of intact impressions \vas measured indirectly on stone dies. Finally, a siniplt% rntxthod to avoid deformation of elastic impressions in soft copper bands evolved.