Dimensional stability and dehydration of a thermoplastic polycarbonate-based and two PMMA-based denture resins.

This study compared the dimensional stability and dehydration of a thermoplastic polycarbonate denture base resin with two conventional polymethyl methacrylate denture base resins. Maxillary complete dentures were fabricated from the three denture materials and the accuracy of fit along the posterior palatal border of the cast used in processing was measured. Measurements were conducted at five palatal locations immediately after processing and at 7 and 30 days during immersion in water (23 degrees C) and at 7 and 30 days during dehydration (23 degrees C, 65-75% relative humidity). Percentage mass loss during dehydration was determined with an electronic balance. The thermoplastic material was separately compared with each of the conventional resins using a modified Welch two-sample t-test, with a Bonferroni correction for P values. For mean palatal dimensional change, the thermoplastic resin was generally not statistically different from the conventional resins after processing and during immersion (P > or = 0.06), but was generally less than the conventional resins during dehydration (P < or = 0.02). For mean percentage mass loss, the thermoplastic resin consistently showed much smaller, statistically significant values compared with the conventional resins (P < 0.001). It was concluded that the thermoplastic resin should show dimensional changes in service comparable with the conventional resins, but less dimensional change caused by dehydration.

Improved fit of maxillary complete dentures processed on high expansion stone casts.

PURPOSE: Although relatively well-fitting dentures are produced at low cost and with easy-to-manipulate material, current denture base materials are not ideal. Because acrylic resin complete and removable partial dentures change dimensionally as a result of polymerization and thermal contractions, a high expansion stone was tested in this study to determine its ability to compensate for some of the dimensional change. MATERIAL AND METHODS: Maxillary complete dentures were processed on type III dental stone and high expansion stone casts. The accuracy of fit along the posterior palatal border was measured and compared after the prostheses were trimmed and polished and after their immersion in water at 23 degrees C at 1-day and 1-week intervals. RESULTS: Statistical analysis of the data revealed that at every measurement interval the maxillary complete dentures processed on high expansion stone had posterior palatal border openings that were significantly smaller when compared with type III dental stone (p < 0.001).

Posterior palatal seal adaptation: influence of a high expansion stone.

In this follow-up investigation, the ability of a new, high expansion stone to reduce acrylic resin denture base processing distortions was studied and compared with a previously reported investigation of bases processed on buff stone. Denture bases were processed by the continuous-injection and trial-pack techniques on flat vault palate casts and then trimmed and polished. Measurements were made at the posterior palatal border opening at 1 day and 1 week immersion in water (23 degrees C). Results showed that denture bases processed on high expansion stone had better posterior palatal seal adaptation compared with those processed on buff stone, independent of processing techniques.

Removable partial denture design by Canadian dental laboratories: a retrospective study.

Identical, unilateral, distal extension base (DEB) maxillary and mandibular casts with a posterior modification area were mailed to 15 Canadian commercial dental laboratories. Each cast was accompanied by a letter explaining the purpose of the study and a request for the laboratory to design a RPD-U and RPD-L framework. The package also included a questionnaire on the techniques commonly used by dentists in the construction of a removable partial denture prosthesis, as well as the laboratory procedures they requested from laboratory technicians. Compared to the findings of previous studies by McCracken and others, the results of this study indicate an improvement in the dentists' understanding of the fundamental principles of an RPD framework design. However, the questionnaire also revealed the need for improved communication between the dentist and the technician. The study suggests that the basic principles for the construction and design of removable partial dentures, as taught in dental schools across Canada, must be respected by dentists.

Esthetic considerations in the construction of a removable partial denture.

In the construction of a removable partial denture, the patient's interest frequently lies in the improvement of his or her esthetic appearance. This desire can be underestimated by the scientifically trained dentist, resulting in a disappointed patient. The perimeters of potential esthetic improvement might be influenced by the limitations of each individual case. However, appropriate care in the selection, arrangement, and position of teeth can overcome some of the limitations. This article describes the benefits of a well-planned, systematic approach to selection of the framework design, porcelain shade, and tooth mold as well as the base finish, and it illustrates, with specific examples, how to achieve the maximum esthetics in removable partial denture prosthodontics.

Posterior palatal seal adaptation: influence of processing technique, palate shape and immersion.

Accuracy of fit of denture bases is critical to adequate retention. This study compared the dimensional change of a newer continuous-injection technique with a standard trial-pack technique as determined by measuring the posterior palatal border opening. The influence of palate shape and immersion were also assessed. Stone casts were made from master moulds with either a high or flat palate. Denture base adaptation was measured at 5 mm intervals across the entire posterior palatal border. Measurements were made after deflasking, trimming and polishing, and after immersion in room temperature water for 1 h, 1 day and 1 week. Statistical analysis (P < 0.05) showed that where differences occurred between the two techniques, openings were always smaller for the continuous-injection technique. It was also shown that dimensional changes were always larger for the flat palate compared with the high palate. Dimensional change using the continuous-injection technique was reduced by immersion in water, while no influence was observed for the trial-pack technique. It was concluded that the continuous-injection technique showed smaller dimensional changes compared with the standard trial-pack technique, and that these changes were influenced by palate shape and immersion in water.

Comparison of the dimensional stability of two waxes and two acrylic resin processing techniques in the production of complete dentures.

Two base plate waxes and two denture processing techniques were independently compared for dimensional stability. Occlusion rims were constructed from extra hard and medium soft base plate waxes and teeth were set. Acrylic resin bases were processed by a trial packing technique, and a continuous injection system. Tooth movement was measured in the horizontal and vertical planes to assess wax and denture base dimensional changes at various steps in the process, and after 1, 3, and 8 weeks of denture base immersion in water at room temperature. Posterior palatal border adaptation, incisal pin opening and loss of centric occlusion contacts, were also measured. Results showed there were no significant differences between the two waxes as determined by tooth movement in the horizontal and vertical planes. In comparison to the trial packing technique, the continuous injection system showed significantly smaller changes for incisal pin opening and loss of centric occlusion, and better adaptation of the posterior palatal border to the cast. Measurement of tooth movement in the horizontal and vertical planes showed no significant differences between the two processing techniques for times prior to immersion in water, whereas after 8 weeks immersion the continuous injection technique showed smaller dimensional changes, relative to the original dimensions at the time of investing.

Dental technology education in Canada.

The dental technology education in Canada is described through a brief introductory historical overview with the emphasis placed on the present status of dental technology teaching institutions, accreditation system, admission policies, curriculum content, requirements for registration or certification and the comparison of provincial board examinations. The role and the responsibility of organized dentistry is stressed on shaping the future trends in dental technology.