Comparison of vertical movement occurring during loading of distal-extension removable partial denture bases made by three impression techniques

Digital comparative analysis in three dimensions of two impression techniques for the bilateral distal extension of partially edentulous mandibular arches: A pilot clinical study

STATEMENT OF PROBLEM

The stability of mandibular removable partial dentures with bilateral distal extensions may be improved with the controlled tissue support achieved by using the altered cast impression technique, although this process is time-consuming and technique-sensitive.

PURPOSE

The purpose of this pilot clinical study was to compare casts generated from a conventional definitive impression with casts generated from an altered cast impression using a 3-dimensional (3D) analysis software program.

MATERIAL AND METHODS

Three partially edentulous participants with mandibular Kennedy Class I were enrolled, and impressions were made with the 2 techniques and poured in stone. The casts were scanned, aligned, and superimposed by using a 3D analysis software program. Surface deviations were measured to evaluate the differences in displacement induced by the impression on the tissue surface. Five observations were made in 4 different areas on each partially edentulous side. Means from these observations were generated, and the Wilcoxon and Mann Whitney tests were performed for all data to assess the differences between the right and left sides in the same participant and among the 3 participants (α=.05).

RESULTS

The casts made from the altered cast impression had an overall mean ±standard deviation displacement of -0.05 ±1.25 mm on the right and left sides of the mandibular buccal shelf area. Moreover, the greatest overall difference of about 0.45 ±0.41 mm occurred on the lingual slope of the residual ridge, and the differences in the other areas were 0.10 ±0.99 mm (crest of the residual ridge) and 0.16 ±0.66 mm (buccal slope of the residual ridge). The overall differences varied statistically between significance and nonsignificance for the same participant and among the 3 participants.

CONCLUSIONS

A digital comparative analysis of the conventional and altered cast methods of recording the bilateral distal extension areas in partially edentulous participants showed that the altered cast method exhibited more displacement on the buccal vestibule or buccal shelf area compared with other examined areas. The differences between the 2 impression methods in the displacement values among the examined areas were minimal and in close proximity, and such differences may lack clinical significance.

A novel digital altered cast impression technique for fabricating a removable partial denture with a distal extension

BACKGROUND

Although computer-aided design and computer-aided manufacturing has been successfully used in fabricating removable partial dentures (RPDs), making altered cast impressions is still a time-consuming and labor-intensive process for fabricating RPDs with a distal extension. An alternative digital technique has been developed to simplify this process.

METHODS

The authors present a case in which they sought to improve the efficiency and simplicity in obtaining altered cast impressions by means of digital technology. Initially, a primary plaster cast was scanned as a digital cast. Based on the digital cast, a novel custom tray was designed and fabricated using a 3-dimensional printing method. With the custom tray, the novel altered cast impression was fabricated and scanned, and the final virtual altered cast was reconstructed by a stitching method.

RESULTS

Based on the virtual altered cast, the authors designed the virtual RPD framework. Finally, the titanium alloy framework was fabricated using a 3-dimensional printing process, and the authors fit the final RPD to the patient.

CONCLUSIONS

This novel digital altered cast impression technique may eliminate interoperator variability and increase precision compared with the traditional technique.

PRACTICAL IMPLICATIONS

This technique showed the potential for reducing clinical appointments, chair time, and laboratory procedures.

Biomechanics of oral mucosa

The prevalence of prosthodontic treatment has been well recognized, and the need is continuously increasing with the ageing population. While the oral mucosa plays a critical role in the treatment outcome, the associated biomechanics is not yet fully understood. Using the literature available, this paper provides a critical review on four aspects of mucosal biomechanics, including static, dynamic, volumetric and interactive responses, which are interpreted by its elasticity, viscosity/permeability, apparent Poisson's ratio and friction coefficient, respectively. Both empirical studies and numerical models are analysed and compared to gain anatomical and physiological insights. Furthermore, the clinical applications of such biomechanical knowledge on the mucosa are explored to address some critical concerns, including stimuli for tissue remodelling (interstitial hydrostatic pressure), pressure–pain thresholds, tissue displaceability and residual bone resorption. Through this review, the state of the art in mucosal biomechanics and their clinical implications are discussed for future research interests, including clinical applications, computational modelling, design optimization and prosthetic fabrication.

A comparative study of impression procedures for distal extension removable partial dentures

AIM

This study was carried out with the purpose of comparing three impression methods as to which of them placed tissues most favorably.

METHODS

The methods used were Hindels method, selective tissue placement method and functional reline method. The measurements obtained were analyzed to determine which of the three impression methods placed the mucosal tissues maximally. To compare and measure tissue placements, autopolymerizing acrylic resin platforms were constructed to the height of the occlusal surfaces of the remaining teeth. 15 orthodontic buccal tubes were placed on each side of the platform. They were arranged in three sets of five and attached to the platform over selected reference regions by means of autopolymerizing resin. The selected reference areas were in anterior, middle and posterior areas of the ridge on either side.

RESULTS

No significant difference was seen in tissue placement in the anterior middle and posterior regions in each of the three methods when each method was assessed separately. Selective tissue placement method placed the tissues maximally (7.547 mm) followed by Hindels method (7.2110 mm) and the least placement was by functional reline method (5.856 mm). Tissue placement was significantly higher in Hindels method as compared to functional reline method (p < 0.001).

CONCLUSION

Tissue placement was maximum in the posterior region, followed by the middle region and least in the anterior region of the mandibular ridge for all three methods. Selective tissue placement method showed the maximum overall tissue placement followed by the Hindels method and minimum placement was by functional reline method.

CLINICAL SIGNIFICANCE

Selective tissue placement method provided maximum overall tissue placement and can be a preferred technique for impression making for bilateral distal extension removable partial denture fabrication.

The bases for using a particular occlusal design in tooth and implant-borne reconstructions and complete dentures

OBJECTIVES

A systematic review identified randomised and other trials (1966-2006) of studies of occlusal design of crowns, complete (CRP) and partial (PRP) removable prostheses and implant-borne reconstructions, and whether occlusal design influenced diet, quality of life, bruxism and attrition.

METHODS

The search primarily included Cochrane Database of Systematic Reviews and Central Register of Controlled Trials, Database of Abstracts of Reviews of Effectiveness, Ovid Medline and PreMedline.

RESULTS

The search yielded 1315 studies: 20 on CRP--1 RCT, one systematic review, four clinical trials, 10 case series; 22 on PRP - one cohort study, two experimental studies, 15 case reports or case series, three clinical trials; 23 on implant superstructures, and 24 reports on implant failure, 37 on oral health related quality of life, eight on attrition; and four studies on masticatory function.

CONCLUSIONS

CRP--Studies of occlusal form and tooth arrangements, included balanced, lingualised and monoplane arrangements--lingualised posterior occlusion was preferred. Early studies on CRP design were observational as case reports, however data suggested that optimum function is achieved by modification of the maxillary occlusion, irrespective of the opposing mandibular occlusion. PRP--Edentulous ridge resorption is patient-specific, has a multifactorial aetiology and there is no objective data to confirm that mechanical factors cause bone loss; oral hygiene management is crucial for long-term health. Studies on distal extension PDs confirmed a link between bite force and masticatory function; preservation of two functioning posterior tooth units ipsilateral to the distal extension optimises function. Data indicate that patient-specific factors, rather than PD design-specific features, influence long-term PD outcomes. Implant superstructures--There is little scientific evidence specifying occlusal and superstructure design for fixed prostheses for teeth or implants. Occlusal scheme design and occlusal form have evolved through clinical experience, but there is no evidence to indicate that a particular design is superior. Complex neurophysiological mechanisms allow the jaw muscle system to accommodate to oral and dental changes.

Clinical evaluation of abutment teeth of removable partial denture by means of the Periotest method

Prosthodontics should be one of the means of establishing conditions for the maintenance of periodontal health. The forces applied to the abutment teeth and their effects are very important considerations in the design and construction of the removable partial dentures. This 6-month follow-up clinical study evaluated the degree of mobility of abutment teeth of distal extension and tooth supported removable partial dentures by using Periotest. Two types of clasp design were selected for evaluation. In cases with unilateral and bilateral distal-extension, a clasp design including a T clasp of Roach retentive arm, a rigid reciprocal arm and a mesial rest were used. For the abutments of tooth-supported removable partial dentures, a second clasp design with a cast circumferential buccal retentive arm, a rigid reciprocal clasp arm and a rest adjacent to the edentulous ridges was selected. A total of 68 abutment teeth was analysed. Periotest values were made at the time of denture placement (control) and at 1, 3 and 6 months after the denture placement. The statistical analysis was performed using Friedman test. All analysis was performed at a 0.05 level of significance. The results revelled that no significant changes in tooth mobility were observed during the 6-months follow-up (P > 0.05). In conclusion, our findings suggest that adequate oral hygiene instructions, careful prosthetic treatment planning and regular recall appointments play an important role in preventing changes in abutment tooth mobility caused by removable partial denture placement.

Direct tissue stops for distal extension removable partial dentures

Supplemental impression++ strategies may be used to capture optimal registration of residual ridge tissues in distal extension-base RPDs. A procedure is described to adapt tissue stops in vivo and positively position the framework to the master cast when clinically using corrected impressions. This method is simple and cost-effective, and it promotes accurate prosthetic-tissue relationships during clinical and laboratory phase of RPD fabrication.

Sectional impressions for mandibular distal extension removable partial dentures

STATEMENT OF PROBLEM

Corrected impression procedures provide the best possible support to be gained from an edentulous ridge for a removable partial denture, but they are time-consuming and technique-sensitive.

PURPOSE

An experimental mandibular distal extension removable partial denture was used to measure the vertical movement of denture bases during biting.

MATERIAL AND METHODS

Five patients participated for whom vertical movement of denture bases was measured by comparing the thickness of plaster interocclusal records made with the denture at rest and under biting pressure. Denture bases were processed on master casts formed from final impressions made in full arch custom trays. Secondly, bases were readapted using sectional relining impressions with the same regular body polysulfide impression material.

RESULTS

Statistical analysis of the vertical movement of denture bases during biting at 4 points on the right and left denture bases showed a significant decrease in vertical movement with sectional impression. The reduction was less than a 0.1 mm, a result that questions the routine use of sectional impression for every distal-extension mandibular removable partial denture.

CONCLUSION

Supportive form of distal-extension edentulous ridges can be recorded successfully by full arch impressions in custom trays.

Selective-pressure single impression procedure for tooth-mucosa-supported removable partial dentures

This article describes a method of making impressions for tooth-mucosa-supported removable partial dentures using a single impression procedure. Through the use of border-molded custom trays, selectively relieved, and application of pressure on residual ridge areas, the objectives of maximum tissue coverage and selective tissue placement of primary stress-bearing areas are fulfilled. With a single impression procedure, treatment time is reduced and laboratory errors commonly encountered with the altered cast impression technique can be minimized or eliminated.

Effect of splinting on load distribution of extracoronal attachment with distal extension prosthesis in vitro

Previous reports have suggested that the restoration of distal extension edentulous areas with an extracoronal precision attachment partial denture necessitates splinting of abutments. However, the number of splinted teeth remains controversial. In this study, strain gauge technology was used to monitor stresses induced around the abutment and in the distal extension area under different loads as a function of the number of splinted abutments. Three strain gauges were installed in the outer buccal, lingual, and distal surfaces of the abutment to record stresses in the three planes of motion, and another gauge was placed under the distal extension base. The reduction of the number of splinted units from three to two resulted in an insignificant increase of stresses recorded, whereas reduction of the number from two to one resulted in a significant increase of stresses nine times greater than the three-unit splint values. On the basis of this in vitro model, at least two teeth on each side should be splinted when extracoronal distal extension attachment prostheses are used.

Vertical distortion in distal extension ridges and palatal area of casts made by different techniques

A coordinate measurement machine with laser probe was used to measure the vertical distortion of the casts produced by use of three types of impression materials (irreversible hydrocolloid, condensation silicone, and addition silicone) and two types of trays (stock and custom trays). Results indicated that all impression groups showed positive vertical distortion (ranging from 0.00566 to 0.30299 mm) at the edentulous ridges and palatal area. The amount of the vertical distortion was greatest at the palatal area and was followed by the high edentulous ridge and the low edentulous ridge. Addition silicone, with either custom tray or stock tray, was the most accurate impression material. Condensation silicone was more accurate than irreversible hydrocolloid in custom tray impression. However, in stock tray impression the irreversible hydrocolloid was more accurate than the condensation silicone. The results suggest that, with careful manipulation, irreversible hydrocolloid with stock tray impression may provide a satisfactory cast for fabricating the framework of a distal extension removable partial denture.

Evolution of removable partial denture design

This is a brief overview of the progress of design philosophies of removable partial dentures. It begins in 1711 with the first published description of a removable partial denture prosthesis and continues, with discussion of the most significant discoveries, through 1990.