Comparison of the linear dimensional accuracy of the maxillary denture teeth by three flask closure methods. An in vitro study

PURPOSE

This laboratory study conducted to evaluate and compare the influence of different flask closure methods on linear dimensional changes of standardized simulated maxillary complete dentures.

MATERIALS AND METHODS

Thirty casts were made from a silicone mold representing an edentulous maxillary arch. Thirty identical maxillary dentures were made and randomly assigned to 3 test groups (A, B, C). In Group A, flasks were placed directly in pressure clamp after trial closure. Group B: The final closure was done in a hydraulic press then transferred to pressure clamp. Group C: After trial closure flask was positioned between the two iron plates of the Restriction System flask closure (RSFC) method. Then linear distances were measured three times before and after polymerization: right incisor to left incisor (RI-LI), right premolar to left premolar (RPM-LPM), right molar to left molar (RM-LM) and left incisor- to- left molar (LI-LM) and right incisor- to- right molar (RI-RM) with the help of digital caliper with an accuracy of 0.01mm. ANOVA and Tuckey's test were used to compare the groups (p < 0.05).

RESULTS

Inter molar (LM-RM) width showed the greatest dimensional change after processing and Linear dimensions were not significantly influenced by the packing procedure.

CONCLUSION

Within the limitations of this study, Restriction System flask closure (RSFC) method demonstrated a similar performance in reducing the tooth movement when compared with other flask closure methods. The posterior region of the denture may present changes in the tooth position after processing, which need to be clinically adjusted.

Credibility and Confidence in Your Dental Laboratory Work-How Quality Assurance Systems Can Be Used in the Manufacturing of Individual Custom-Made Dental Devices

Manufacturing of custom-made dental devices such as removable dentures, fixed prosthodontics and orthodontics are subject to the requirements of the Medical Devices Directive (MDD). Many dental laboratories often enhance these requirements by implementing quality assurance procedures that then provide enhanced consistency. This paper provided a personal view of some of the systems currently being used in dental laboratories to provide a quality assured product and associated issues.

Complete Dentures: Designing Occlusal Registration Blocks to Save Clinical Time and Improve Accuracy

The techniques described in this article are based on facial measurements and an analysis of the patient's existing dentures to provide measurements that will enable registration blocks to be constructed for individual patients rather than the arbitrarily produced block more commonly seen. Employing the methods shown will lead to a saving in clinical time and contribute to a more accurate registration. It is important to remember that the technician can only provide occlusal registration blocks of the appropriate dimensions if the clinician has assessed the patient and existing dentures and then passed this information to the laboratory. Clinical Relevances: Being able to assess the clinical suitability of a patient's existing dentures and then take measurements from those dentures will allow occlusal registration blocks to be constructed that have the correct dimensions and anatomical features for a particular patient. This will save time during the registration stage and help to improve accuracy.

Dentures for Randomised Controlled Trials

Making complete dentures for dental research is difficult. The difficulty is not in the construction of dentures, but making sure the clinician is blind to the randomizations, and avoiding confounding variables. For research purposes it is essential that two sets of dentures are similar in every way, apart from the area to be investigated. A previous article showed how to duplicate a lower denture when it was articulated against a single upper denture. This paper describes the additional duplication of upper dentures. These additional problems presented the clinical and technical teams at the Leeds Dental Institute some challenges.

Electronic laboratory quality assurance program: A method of enhancing the prosthodontic curriculum and addressing accreditation standards

STATEMENT OF PROBLEM

An electronic quality assurance (eQA) program was developed to replace a paper-based system and to address standards introduced by the Commission on Dental Accreditation (CODA) and to improve educational outcomes. This eQA program provides feedback to predoctoral dental students on prosthodontic laboratory steps at New York University College of Dentistry.

PURPOSE

The purpose of this study was to compare the eQA program of performing laboratory quality assurance with the former paper-based format.

MATERIAL AND METHODS

Fourth-year predoctoral dental students (n=334) who experienced both the paper-based and the electronic version of the quality assurance program were surveyed about their experiences. Additionally, data extracted from the eQA program were analyzed to identify areas of weakness in the curriculum.

RESULTS

The study findings revealed that 73.8% of the students preferred the eQA program to the paper-based version. The average number of treatments that did not pass quality assurance standards was 119.5 per month. This indicated a 6.34% laboratory failure rate. Further analysis of these data revealed that 62.1% of the errors were related to fixed prosthodontic treatment, 27.9% to partial removable dental prostheses, and 10% to complete removable dental prostheses in the first 18 months of program implementation.

CONCLUSIONS

The eQA program was favored by dental students who have experienced both electronic and paper-based versions of the system. Error type analysis can yield the ability to create customized faculty standardization sessions and refine the didactic and clinical teaching of the predoctoral students. This program was also able to link patient care activity with the student's laboratory activities, thus addressing the latest requirements of the CODA regarding the competence of graduates in evaluating laboratory work related to their patient care.

How good are our impressions? An audit of alginate impression quality in the production of removable prostheses

Impressions are taken regularly in practice giving vital information to the dental laboratory, but are there quality assurance systems in place to make sure that they are up to a sufficient standard? As dental professionals we have to appreciate that dental technicians can only work with the information given to them. This makes the skill of taking a good impression vital in order for us as clinicians to provide prostheses of good quality. This paper outlines an audit of alginate impressions and their quality in the making of removable prostheses.

CLINICAL RELEVANCE

To record the quality of impression taking, and how one's own ability to critique an impression may differ from that of our colleagues.

[Removable prosthesis insertion steps: controls-qualifications]

Support a prosthetic edentulous patient aims to optimize the rudimentary functions of mastication and phonation. Knowing the routine procedures in dentistry is needed. These prostheses can be a source of criticism in terms of the quality of life they provide. Chronologically, several steps must be followed when delivered: Reception at the dental office of the prosthesis, with its technical specifications, Meticulous checks prosthetic surfaces, Introduction in the oral cavity of dentures smoothly, The stability of the prosthesis is tested initially, Second occlusion is checked, The esthetic of the prosthesis previously endorsed in the fittings, is popular again, Phonetic tests are performed to help verify the positioning of the teeth in relation to the lips, Tests for judging the ability to swallow, to incise and biting at the posterior teeth are made by the patient, Check alignment of mounting the entire face, Follow the recommendations for proper use of the prosthesis. The complementarily of these steps determines the integration of the prosthesis, but the patient must be informed early in the treatment of functional and aesthetic limits of its future prosthesis.

Implementation of a laboratory quality assurance program: the Louisville experience

Remakes, or the refabrication of dental prostheses, can occur as a result of inherent inaccuracies in both clinical and laboratory procedures. Because dental schools manage large numbers of predoctoral dental students with limited familiarity and expertise as related to clinical prosthodontic techniques, it is likely these schools will experience an elevated incidence of laboratory remakes and their ramifications. The University of Louisville School of Dentistry, not unlike other dental schools, has experienced remakes associated with both fixed and removable prosthodontic procedures. Limitations in faculty standardization and variable enforcement of established preclinical protocols have been identified as variables associated with the high percentage of remakes documented. The purpose of this study was to introduce the implementation of a new multidepartmental quality assurance program designed to increase consistency and quality in both information provided to commercial dental laboratories and the prostheses returned. The program has shown to be advantageous in terms of cost-effectiveness and treatment outcomes. A statistically significant decrease in remake percentages has been recorded from inception of this program in December 2010 until December 2012. Furthermore, this program has resulted in more consistent communication between the dental school and commercial dental laboratories, among faculty members, and between faculty and students.

[Complete removable dentures: a commitment to best efforts]

The provision of complete removable dentures can, in legal terms, be defined as a commitment to perform the best of one's abilities. Indeed, the result or patient's satisfaction with the new dentures, is difficult to predict and is apparently not only dependent upon the dentist/denturist and variations in materials and techniques. The relationship between the dentist/denturist and the patient is complex, but influences to a large extent patient satisfaction. This is especially true in cases of patients with reduced residual alveolar ridges or other (oral) problems. When a complete removable denture is being prepared, the patient should be thought of as the dentist/denturists most reliable contributor. By way of preventing or preparing for possible legal procedures, a good patient record is of importance. The patient record should contain the information which the patient has provided, the patient's request for help, and the character of the patient's expectations for treatment.

Implant overdentures: dental students' performance in fabrication, denture quality, and patient satisfaction

The purpose of this study was to evaluate dental students' performance when fabricating a mandibular two-implant overdenture (OD) as compared to conventional dentures (CD) and to determine if these prostheses were successful. Twenty students and twenty patients were divided into two groups: complete denture group (CDG) and maxillary denture and two-implant OD group (ODG). Students' progress was evaluated at each appointment as they were given a clinical assessment score (CAS), which varied from 1 (unacceptable, needs to repeat procedure) to 4 (acceptable, no errors). The success of the prosthesis was evaluated by the patients using a visual analog scale (VAS) and an expert (a prosthodontist) using a denture quality assessment (DQA) form. Performance for both groups was not statistically different across all eight appointments (CDG 3.16 versus ODG 3.25; p=0.46). Patients with ODs reported greater stability with their dentures (p=0.048) and greater ability to chew than patients with CDs (p=0.03). There were no differences between the groups in terms of expert appraisal (ODG 71.1 versus CDG 67.5; p=0.59). The performance of dental students when fabricating a two-implant OD is thus not different from that of a CD. Students can successfully fabricate a two-implant OD as perceived by both patients and prosthodontists.

Microstructure analysis of dental castings used in fixed dental prostheses--a simple method for quality control

The aim of this study was to evaluate the microstructural quality of noble alloy castings from commercial dental laboratories using the wiping-etching method as a simple method for quality control. In total, 240 castings from two noble alloys (AuAgCuPt and AuPtZn) were taken from a day's production of five different dental laboratories. The casting quality was evaluated by determining the grain size and by assessing the number and size of shrinkage cavities after acidic etching of the alloy surfaces. The AuAgCuPt alloy castings showed an acceptable quality in the microstructural analysis. The results of AuPtZn castings, however, were not satisfactory because 50.8% of the samples showed a remarkably poorer quality compared to the specifications made by the manufacturer. The proportion of the employed reclaimed alloy had no influence on the casting quality when AuAgCuPt alloy was used, but was influential when casting restorations with AuPtZn alloy. When determining the quantity and size of shrinkage cavities, none of the evaluated castings was of such a poor quality that a replacement of the castings had to be considered. The differences in grain size and quantity of shrinkage cavities were reflecting the individual laboratory process rather than the admixture of new/reclaimed alloy. The presented analysis can be used as a simple method for quality control of dental castings.

An audit to assess the quality and efficiency of complete and partial dentures delivered by junior hospital staff

The average number of visits for the construction of metal-based and acrylic dentures by junior hospital staff was 10 visits. Our hypothesis was that supervision would optimise the number of visits and reduce any need for remakes. The first audit cycle was retrospective and included all patients treated by SHOs in the Prosthodontics Department. The standard of care was compared to the British Society for the Study of Prosthetic Dentistry. The re-audit showed that the time taken to completion was reduced by 2 visits for both denture types and the average length of time was reduced from 31 weeks to 22 weeks. These improvements were directly related to improved supervision by senior staff.

Difference in illuminant-dependent color changes of shade guide tabs by the shade designation relative to three illuminants

PURPOSE

To determine the difference in illuminant-dependent color changes of shade guide tabs of Vita Lumin (VITA), Chromascop (CHRO) and Vita 3D-Master (3D-M) shade guides by the shade designation in each shade guide.

METHODS

Color of 16 tabs of VITA, 20 tabs of CHRO and 29 tabs of 3D-M was measured according to the CIELAB color scale relative to the CIE standard illuminant D65, A and F2. Color differences (deltaE*ab) between the A1 tab and other VITA tabs, between the 110 tab and other CHRO tabs and between the 0M1 tab and other 3D-M tabs relative to the three illuminants were calculated, and the ratios of deltaE*ab values relative to the different illuminants [deltaE*ab(A)/deltaE*ab(D65), deltaE*ab(F2)/deltaE*ab(D65) and deltaE*ab(F2)/deltaE*ab(A)] were calculated. Ratios of the hue angle shifts of each shade tab by the change of illuminant over the corresponding value of the Al, the 110 or the 0M1 tab were also calculated. Differences in the ratios of color difference and hue angle shift were analyzed with a repeated measures, two-way analysis of variance (alpha = 0.05).

RESULTS

Ratios of deltaE*ab values by the illuminant were 0.90-1.17, 0.95-1.07 and 0.99-1.06 for the VITA, the CHRO and the 3D-M shade guide, respectively. Ratios of the hue angle shifts by the illuminant were from -1.6 to 1.8 for the VITA, from -7.3 to 1.2 for the CHRO and from -1.2 to 3.1 for the 3D-M. Changes in color and hue angle of shade tabs were significantly different by the shade tab designation when illuminant was changed (P < 0.01).

Effect of the quality of removable prostheses on patient satisfaction

AIM

The objective of this study was to evaluate patient satisfaction with removable prostheses and its relationship with denture quality.

METHODS AND MATERIALS

Sixty-seven patients who received 119 new removable prostheses over a period of one year at the College of Dentistry, King Saud University, were recalled for an interview with regard to their satisfaction with their dentures and a clinical examination. Prosthetic quality was determined using the California Dental Association criteria.

RESULTS

Results showed 75% and 66% of upper and lower dentures, respectively, were reported by patients as satisfactory. Of all the upper prostheses rated as being of acceptable quality, 94% were also reported by patients as satisfactory, but of those of unacceptable quality, only 52% were reported by patients as unsatisfactory. The corresponding figures for lower dentures were 91% and 71%, respectively. No significant associations were found between patient satisfaction and age, or denture experience.

CONCLUSION

Although acceptable quality of removable prostheses usually resulted in patient satisfaction, the finding that some patients were satisfied with their prostheses despite unacceptable quality suggests other factors besides quality affect outcomes.

CLINICAL SIGNIFICANCE

Patient satisfaction with removable dentures cannot be fully predicted from only the quality standards of those dentures.

A methodology to study the effects of prosthesis misfit over time: an in vivo model

PURPOSE

Passive fit of implant-supported superstructures cannot currently be achieved. The aim of this investigation was to create a methodology that can be used to study the effects of prosthesis misfit in humans.

MATERIALS AND METHODS

An edentulous patient received two interforaminal implants and a screw-retained bar for the retention of the mandibular denture. A corresponding in vitro model with strain gauges placed mesially and distally, adjacent to the implants, was fabricated to serve as a standardizing control. Over a period of 6 months, a total of 10 measurements on both the in vitro model and in the patient's mouth were conducted with newly fixed strain gauges on the bar.

RESULTS

The in vitro experiments showed that no component wear at the abutment-bar interface had occurred and that repositioning of the strain gauges on the bar caused deviations in strain measurements up to 10.55%. In vivo, a reduction in strain development, from 445 to 383 Mum/m, was observed in the initial phase up to 12 weeks after bar insertion. Subsequently, the measurement values increased, and after a period of 24 weeks, they nearly reached the initial strain level (443 microm/m). Only minor changes in strain development of the bar could be detected; these might be a result of limited dynamic loading and the cortical architecture of the surrounding bone. Deviations in measurement accuracy caused by repositioning of the bar strain gauge are a limitation of this technique and should be eliminated in future studies.

CONCLUSIONS

The present methodology can be applied to study changes in static implant loading over time in humans.

A clinical pathway for complete immediate denture therapy: successful prosthetic management for hopeless dentitions

This article presents a rationale for utilizing complete immediate denture therapy, highlighting various advantages, disadvantages, and contraindications for this treatment. Jerbi's technique for presurgical cast carving is reviewed and a unique case report is detailed, involving a 22-year-old patient whose hopelessly debilitated dentition was treated by full-mouth extraction and placement of a maxillary and mandibular complete immediate denture. In addition, a brief review of changing dietary patterns and social habits is presented in relation to the recent escalation of rampant dental caries in youth and young adult patient populations.

Fracture strength of two oxide ceramic crown systems after cyclic pre-loading and thermocycling

The aim of the present study was to investigate the fracture resistance of zirconia crowns and to compare the results with crowns made of a material with known clinical performance (alumina) in away that reflects clinical aspects. Sixty crowns were made, 30 identical crowns of alumina and 30 of zirconia. Each group of 30 was randomly divided into three groups of 10 crowns that were to undergo different treatments: (i) water storage only, (ii) pre-loading (10 000 cycles, 30-300 N, 1 Hz), (iii) thermocycling (5-55 degrees , 5000 cycles) + pre-loading (10 000 cycles, 30-300 N, 1 Hz). Subsequently, all 60 crowns were subjected to load until fracture occurred. There were two types of fracture: total fracture and partial fracture. Fracture strengths (N) were: group 1, alumina 905/zirconia 975 (P = 0.38); group 2, alumina 904/zirconia 1108 (P < 0.007) and group 3, alumina 917/zirconia 910 (P > 0.05). Total fractures were more frequent in the alumina group (P < 0.01). Within the limitations of this in vitro study, it can be concluded that there is no difference in fracture strength between crowns made with zirconia cores compared with those made of alumina if they are subjected to load without any cyclic pre-load or thermocycling. There is, however, a significant difference (P = 0.01) in the fracture mode, suggesting that the zirconia core is stronger than the alumina core. Crowns made with zirconia cores have significantly higher fracture strengths after pre-loading.

Considerations for services from dental technicians in fabrication of fixed prostheses: A survey of commercial dental laboratories in Thessaloniki, Greece

STATEMENT OF PROBLEM

Effective communication and cooperation between dentists and dental technicians are essential in providing quality services. There has been a lack of information regarding dentist-dental technician communications and current methods and materials used for the fabrication of fixed partial dentures (FPDs).

PURPOSE

This cross-sectional study identified the materials and techniques used for fabrication of FPDs, as well as the status of communication between dentists and dental technicians in Thessaloniki, Greece.

MATERIAL AND METHODS

A questionnaire was developed with 7 sections pertaining to procedures and materials used for the fabrication of fixed prostheses: general questions, infection control, impressions/interocclusal records, die technique/mounting, information from final casts, prostheses design/materials, and communication/shade selection. The questionnaire was anonymous and distributed by the Association of Dental Technicians of Thessaloniki to all member laboratories (228) in the wider province of Thessaloniki, Greece. Due to the absence of normal distribution of the results, frequencies and medians were reported.

RESULTS

Ninety-six of 228 dental laboratories responded (42.1% response rate). Twenty-six percent of dental laboratories did not routinely disinfect incoming items. The dental technicians considered 30% of incoming final impressions and 20% of interocclusal registrations as inadequate. Half of the time (55%) final casts were mounted by technicians on simple hinge articulators. Only 20% of tooth preparations had adequate finish lines. The majority (70%) of fixed restorations were metal-ceramic. Fifty-seven percent of dental technicians considered the delivery time requested by dentists as insufficient.

CONCLUSION

The information provided in this study indicates areas of weakness in communication between dentists and dental technicians, along with areas where both parties should use greater care during clinical and laboratory procedures.

Guidelines for a minimum acceptable protocol for the construction of complete dentures

PURPOSE

To investigate the feasibility of obtaining expert consensus on the prosthodontic principles to be followed when constructing complete dentures, so that any modifications to materials and methods would not sacrifice those principles--a philosophy known as "appropriatech." These principles would then comprise a Minimum Acceptable Protocol (MAP) for complete dentures.

MATERIALS AND METHODS

A Delphi survey technique was used that requested yes/no answers to a variety of statements describing the different stages in the construction of complete dentures. Respondents could also provide comments on any aspect of the questionnaire. The statements were then modified in light of the responses and comments received, and recirculated. Three rounds of questionnaires were used, and only statements achieving a 90% or greater consensus were included in the MAP. The respondents were randomly selected by country from the 2004 membership e-mail list of the International College of Prosthodontists.

RESULTS

Forty-one respondents answered the first questionnaire, 39 the second, and 36 the third. The 75 statements in the first questionnaire were gradually reduced as consensus was reached, and eventually 18 statements remained with 90% or greater agreement.

CONCLUSION

Even though expert opinion is regarded as the lowest level of evidence, there are no other methods available to derive such a protocol, and the Delphi technique was useful in obtaining the consensus. This MAP could now be used to help assess clinical techniques that attempt to reduce time and costs while producing a quality service-in other words, which will conform to the philosophy of appropriatech.

[The registration of false teeth and the others]

The quality control of false teeth should include the control for designing and processing. The registration of false teeth should emphasize particularly on the qualification of the makers, technology management, quality control and the labeling.

Connecting rigidities of various precision attachments compared with the conical crown retained telescope

The purpose of this investigation was to observe the connecting rigidity of various precision attachments and to compare their connecting rigidities with the conical crown retained telescope (CCT). The connecting rigidity of a retainer was assessed using the flexibility test to measure the mesial and distal end displacements. Four precision attachments were analyzed: the dovetail slide attachment beyeler, cylindrical slide attachment, Spang Stabilex and Mini SG. The CCT was used as the control. Although there were many statistically significant differences between the displacements with the various attachments, displacements when vertically loaded were very small: all mesial end displacements were within 3 microm and distal end displacements were 21.4 microm. The largest of the mesial end displacements when horizontally loaded was as large as 44.5 microm (dovetail slide beyeler), while the others were all below 16.5 microm. The same phenomena occurred with the distal end displacements when horizontally loaded: the largest was seen with the dovetail slide beyeler, followed sequentially by the Spang Stabilex, CCT, cylindrical slide, and the Mini SG. The distal displacement with the dovetail slide beyeler was as large as 75.2 microm; those with the others were all below 31.2 microm, with numerous statistically significant differences between the displacements with the various attachments. Thus, connecting rigidities of rigid precision attachments are very similar to CCT, and only the dovetail slide beyeler attachment is too weak to resist horizontal displacement force.

The quality of dental casts used in crown and bridgework

OBJECTIVE

To assess the quality of dental casts used in crown and bridge construction.

DESIGN

Observational cross-sectional study of dental casts.

SETTING

Commercial dental laboratories and a university dental hospital laboratory in the UK.

MATERIALS AND METHODS

A sample (n = 150) of working and opposing casts used for crown and bridgework prescribed by general dental practices and a dental hospital were sampled from two commercial dental laboratories and an 'on-site' university dental hospital laboratory respectively. A simple '3 point' assessment scale of quality (good, fair and poor) was used to categorise the casts depending on the clarity of reproduction of soft and hard tissues.

RESULTS

The quality of opposing casts used for articulation purposes was significantly better (P<0.001) than that of the working casts. In addition it was found that for working casts the quality in the preparation area(s) was significantly better (p<0.001) than that in areas remote from preparation(s) in the same arch. In general, the quality of casts in the incisal or occlusal surfaces was better than the buccal and lingual surfaces.

CONCLUSIONS

This study has demonstrated that variation exists in the quality of casts used in crown and bridgework, specifically those used in the construction of indirect restorations and also those used for articulation purposes. This study highlights the need for clinicians to exercise continued vigilance with crown and bridge impressions, and casts, particularly in areas away from the prepared teeth.

Oral health in relation to wearing removable dentures provided by dentists, denturists and laboratory technicians

The aim of this study was to evaluate the oral health of elderly Finnish men wearing removable dentures supplied either by dentists, denturists or laboratory technicians. From a sample of 550 men, 362 subjects were both interviewed and clinically examined. The subjects were asked a range of questions related to their oral health and dentures. Clinical examinations were carried out by one dentist using well-defined criteria and without knowing the information the respective subjects had given in the interview. The 242 denture wearers had a higher frequency (P < 0.001) of mucous membrane lesions (78.7%) than the 120 non-wearers (27.5%). Differences between the denture providers were small, although subjects with dentures provided by dentists had less often most of the recorded mucous membrane lesions than other denture wearers. Coating of tongue and cheilitis angularis were the most commonly encountered lesions. High levels of yeast growth were observed more frequently (P < 0.02) among subjects who had obtained their dentures from dentists (41.3%) than from either denturists (17.1%) or laboratory technicians (18.2%). Among dentate subjects, the average number of remaining teeth was higher (P < 0.05) among those who had obtained their dentures from dentists (8.7) than among subjects wearing dentures from denturists (5.9) or laboratory technicians (6.2). Subjects wearing dentures supplied by dentists had slightly better oral health than other denture wearers. The observed differences can be at least partly explained by dentists' patients having higher number of remaining teeth and also more frequent check-up visits.

Relationship between occlusal plane determinants and craniofacial structures

A cephalometric study was conducted on 34 complete denture wearers to investigate the relationship between the anatomical structures commonly used to determine the occlusal plane and the facial skeletal shape. The results showed no correlation between the shape of the skeletal face, the gonial angle and the length of the mandible versus the location of the retromolar pad, the occlusal plane and Camper's plane. However, a statistically significant linear correlation (P < 0.0001) was found between the facial skeletal shape designated SN POG and the location of Camper's plane. Cephalometric analysis alone cannot determine the location of the occlusal plane in edentulous patients. Intra-oral structures should also be considered.

Treatment with removable partial dentures: a longitudinal study. Part I

The aim of this study was to evaluate the effectiveness of an oral rehabilitation by removable partial denture (RPD). Between 1983 and 1994, 629 patients were provided with an RPD at the Dental School of the Université catholique de Louvain. All the RPDs were constructed with a cobalt-chromium framework. All the treatments were provided by dental students under the supervision of clinical instructors. At recall time (1998-2000), 269 patients could not be reached neither by telephone nor by mail and 27 had died. Consequently, 333 patients were called for clinical examination and 254 of these (76.3%) actually attended. For a total of 292 RPDs fitted for these 254 patients, 218 (74.7%) were still being worn at the time of the check-up. Seventy-four dentures were considered to be 'failures', either because they were replaced by another RPD or by a complete denture, or because they had actually never been worn. The statistical analysis (Mantel-Haenszel and Kaplan-Meier) shows that the number of failures is significantly higher at the lower jaw compared with the upper jaw. Most of the failures are attributable to RPDs with free-end saddles and, in particular, to class I mandibular dentures. The patients are wearing their denture(s) mostly continuously (63.6%) and award a high degree of satisfaction to their denture. In general, the results recorded may be considered as very satisfactory, all the more so as we have no regular recall procedures established at our school and as check-up asked for spontaneously by the patients in the course of the period of observation are most of the time occasional or non-existent.

[Cantilever resin-bonded bridges with one adhesive surface. A review of the literature]

Conventional resin-bonded bridges are designed with adhesive surfaces on both sides of the dummy. As a consequence both abutment teeth are rigidly connected to each other. Loading of the abutment teeth or dummy will lead to wringing forces in the cement. Adhesive bridges with one adhesive surface are actually cantilever bridges. Theoretically this type of bridges will be less prone to wringing forces due to loading. However, long term research into the performance of cantilever resin-bonded bridges (RBBs) is hardly available. The results of research into the longevity of conventional RBBs differ remarkably between Europe, and the United States and Japan. These difference are discussed in this article. This article compares the fixed-fixed design RBBs with the cantilever RBBs. The differences are discussed based on eight articles, the earliest being published in 1991, which are dedicated, completely or partially, to the subject of cantilever adhesive bridges. One can conclude that in The Netherlands RBBs are wrongly considered to be unreliable. On the contrary, they appear to be reliable and predictable restorations provided their preparations meet the right standards. Although a number of authors conclude that cantilever RBBs are performing better than their fixed-fixed design counterparts in similar situations, further research is needed concerning the longevity of this type of adhesive bridges.

Clinical quality of removable dentures provided by dentists, denturists and laboratory technicians

The aim of this study was to evaluate the clinical quality of removable dentures of elderly Finnish men, which had been prepared either by dentists, denturists or dental laboratory technicians. The participants comprised 242 denture-wearing subjects, with 231 maxillary and 177 mandibular removable dentures which had been prepared either by dentists, denturists or dental laboratory technicians. Clinical examinations were carried out without the examining dentist knowing who had provided the dentures. Complete dentures which had been illegally provided by laboratory technicians had significantly poorer retention and fitted less well in tuber and alveolar areas than those provided by either dentists or denturists. Complete maxillary dentures which had been provided illegally by laboratory technicians had significantly (P < 0.01) higher occurrence (90%) of some unacceptable characteristics than those (43%) provided by dentists or denturists. The difference between complete mandibular dentures was also obvious, 86% versus 59%, although statistically non-significant. Of those partial maxillary dentures provided by dentists 53% had some unacceptable characteristics, compared with 80% of those illegally provided by denturists or laboratory technicians (NS). In the case of partial mandibular dentures, 36% of those provided by dentists and 32% of those by denturists or laboratory technicians had some unacceptable characteristic (NS). Illegal provision of removable dentures seemed to be related to decreased clinical quality.

[Study on retention and stability of linear occlusal complete dentures]

OBJECTIVE

To learn retention and stability of linear occlusal complete dentures by investigating the subjective feelings of patient and the value of retention force.

METHODS

Static retention forces of maxillary and mandibular dentures were measured for 25 patients wearing linear occlusal dentures by using Hz-1 retention dynamometer. The subjective feelings of patients in functional state were gained simultaneously through questionnaire.

RESULTS

Linear occlusal dentures demonstrate good retention in static and dynamic state. Among patients with severe resorption of residual ridge (RRR), mandibular linear occlusal dentures (shown good retentive subjective feelings) demonstrate significantly smaller retention force than those with slight or medium degree of RRR. There is no correlation between the subjective feelings and the values of retention forces of mandibular dentures. The subjective feelings of patients wearing new linear occlusal dentures are much better than that of old anatomic occlusal dentures.

CONCLUSION

Linear occlusal dentures improve the performances of dentures by enhancing their stability during mastication movement.

Agreement between clinical measures of quality and patients' rating of fit of existing and new complete dentures

OBJECTIVES

To assess agreement between patients' appreciation of fit and clinical assessment of quality of existing and new complete dentures.

MATERIALS AND METHODS

In each case existing complete dentures at the initial visit and new complete dentures at the first post insertion visit were assessed by a prosthodontist using a validated method for assessing denture quality. Patients rated fit of existing and new complete dentures on four-point scales. Weighted Cohen's kappa and multiple correspondence analyses were the statistical methods employed in this study.

RESULTS

459 patients completed the study. A statistically "fair" level of agreement was found between clinical and patient assessment of dentures. There was close correspondence between dentist and patient appreciation when the existing dentures were rated as poor and when the new dentures were rated highly.

DISCUSSION

A worthwhile level of agreement between patients' appreciation of fit of complete dentures and the clinical assessment of quality of existing and new complete dentures was found. Marked differences in the nature of agreement for patients' and clinicians' rating of new and existing dentures were demonstrated. These results emphasize the importance of denture quality in achieving patient approval.

CONCLUSION

Agreement and correspondence between patient and clinician appreciation of existing and new complete dentures were determined.

Matching point clouds: limits and possibilities

In computer-aided production of fixed dental restorations, the process chain always starts with digitizing, independent of the type of further (data) processing, the material used, and the kind of restoration to be produced. The quality of the digitized data, followed by the influences of further data processing and the production parameters, decisively influence the fitting accuracy of the dental restoration to be fabricated. The accuracy with which individually measured 3D data sets in the form of point clouds can be matched for further processing in one common system of coordinates was the object of the present study. Casts of the maxilla and mandible were digitized in several partial measurements comprising two to three teeth in each case, using an optical three-coordinate measuring system. The individual segments were sequentially aligned to surfaces that were created on the basis of partial point clouds. The mean deviation between surfaces and point clouds was between 1.90 microns and 18.24 microns. The accuracy of the alignment was determined by the RMS (root mean square) error, and was on average 14.2 microns (SD 7 microns) for the maxilla and 17.2 microns (SD 9.4 microns) for the mandible. Combining a larger number of smaller segments did not improve the result, since the errors of the individual registrations are summed in sequential matching. In this study, the errors arising in matching are not negligible and can possibly negatively influence the quality (fitting accuracy) of the restoration produced on the basis of the matched data records.

Accuracy of three corrective techniques for implant bar fabrication

STATEMENT OF THE PROBLEM

Numerous articles emphasize the importance of passivity of implant-prosthetic component interfaces. Nonpassive interfaces can lead to bone loss, abutment fracture, and connecting screw breakage.

PURPOSE

The purpose of this study was to evaluate 3 postcasting techniques for the correction of non-passive fit between a cast bar superstructure and its interface with an implant abutment.

MATERIAL AND METHODS

Thirty implant Hader bars were fabricated based on a metal model composed of two 3.8/4.5 HL PME titanium implant abutments. Initial measurements were collected on the y-axis of the left implant abutment-bar interface by using a M2001ARS toolmaker microscope. Means were calculated from buccal, distal, and lingual measurements on each specimen. Ten specimens were sectioned, indexed, and corrected by casting the same alloy (group 1). Ten specimens were sectioned, indexed, and corrected by soldering (group 2). The last 10 specimens were submitted to 2 cycles of electrical discharge machining on a MedArc M-2 EDM machine (group 3). Postcorrection measurements were collected on the 3 groups. A 1-way ANOVA and a Tukey-Kramer test at a 0.05 significance level were performed on the 3 groups after the corrective techniques.

RESULTS

Initial gap means were 192 microm for group 1, 190 microm for group 2, and 198 microm for group 3. There was a significant difference (P<0.05) in gap means between group 1 (15 microm) and group 2 (72 microm) as well as between group 2 and group 3 (7.5 microm) after each correction technique. No difference was detected between group 1 and group 3.

CONCLUSION

The electrical discharge machining group resulted in the smallest mean gap distance of 7.5 microm, thus meeting the criteria of passive fit (within 10 microm) described in the literature.

Relationship between the standards of removable partial denture construction, clinical acceptability, and patient satisfaction

STATEMENT OF PROBLEM

Little is known about the importance of published fabrication standards in determining the outcome of treatment with mandibular distal extension removable partial dentures in patients of community practices.

PURPOSE

This study describes mandibular partial dentures worn by patients from King County, Wash., and examines the validity of standards of design and fabrication by relating the standards to measures of clinical acceptability and patient satisfaction.

MATERIAL AND METHODS

Eighty-two people treated in private dental practices who responded to a mail survey about satisfaction with a partial denture were examined. Eight standards of fabrication, overall clinical acceptability of the prosthesis, and tissue health were evaluated clinically. Patient satisfaction was assessed by questionnaire. Associations between variables were assessed by contingency tables and odds ratios.

RESULTS

Half the prostheses met 4 or fewer of the 8 standards, and these were responsible for nearly all the displacement of tissue by the framework. Forty-three percent of the dentures (35/82) were rated clinically acceptable. Of the remaining dentures, 38 could be made acceptable by modifications. The remaining 9 dentures needed replacement. Sixty-three percent of the patients examined were satisfied with the dentures. There was a relationship between tissue health and the fabrication standards related to rest form, base extension, stress distribution, and framework fit. This study found no relation between tissue health and other design or fabrication features. None of the standards were found to be related to patient satisfaction.

CONCLUSION

This study found partial support for the validity of design/fabrication standards for removable partial dentures. The most important standards are rest form, base extension, and stress distribution. The standards appear to be unrelated to patient satisfaction.

Comparison of resin-bonded prosthesis groove parallelism with the use of four tooth preparation methods

STATEMENT OF PROBLEM

A precise preparation is required to develop resistance form resulting in mechanical stability of the framework for resin-bonded prostheses (RBPs).

PURPOSE

The effects of 4 methods of tooth preparation (freehand, guiding pin, extraoral parallelometer, and intraoral parallelometer) on the deviation of proximal grooves from a preestablished path of insertion (guide planes) were investigated under clinical conditions.

MATERIAL AND METHODS

Tooth preparation of proximal grooves was performed by 32 dentists on resin substitutes of posterior segments intraorally with a single test patient. A Latin-square randomized cross-over design was selected as the experimental design.

RESULTS

The significant least angular deviation of proximal grooves from path of insertion was achieved with an intraoral parallelometer (mean +/- SD 3.15 +/- 1.67 degrees). Compared with freehand tooth preparations (4.37 +/- 2. 11 degrees), neither use of a guiding pin (4.10 +/- 1.62 degrees) nor an extraoral parallelometer (5.06 +/- 2.33 degrees) improved the results.

CONCLUSION

Divergence of guiding grooves from path of insertion was reduced with the use of an intra-oral parallelometer. This should improve mechanical stability of posterior RBPs.

Assessing the quality of clinical procedures and technical standards of dental laboratories in fixed partial denture therapy

PURPOSE

This study was conducted to assess the quality of impressions and tooth preparations sent to dental laboratories in Jordan and to determine the technical capabilities of these laboratories to construct fixed partial dentures.

MATERIALS AND METHODS

A sample of 136 impressions and stone casts were examined for clinical errors in 35 laboratories that construct fixed partial dentures. They were sorted into unusable, unsatisfactory, acceptable, or satisfactory categories. The type of impression material and tray, opposing arch impressions, and occlusal records were noted. Instructions to technicians were assessed for completeness and clarity. Information regarding laboratory staff and equipment were collected.

RESULTS

Half of the specimens inspected were categorized as unusable or unsatisfactory; these were found in commercial laboratories. They showed at least one clinical error such as drags or indefinite finishing lines in impressions and inadequate reduction, undercuts, or obvious taper on stone casts. Alginate impression material was used for 65% of the cases. Only 27% of specimens were accompanied with instructions; of these 22% were graded poor. No occlusal records were available with 54% of the specimens and no articulators were used except in dental school laboratories. The dental schools and some commercial laboratories had the best staff and equipment and were more capable of fabricating fixed partial dentures than those of the Ministry of Health and the Royal Med cal Services.

CONCLUSION

The quality of abutment preparation and impressions were unsatisfactory or unusable in 50% of cases. Of the 37 available instructions 8 were not clear. The dental schools and some commercial laboratories were technically capable of producing good quality fixed partial dentures.

Thermal cycling distortion of porcelain fused to metal fixed partial dentures

STATEMENT OF PROBLEM

The initial fit of porcelain fused to metal restorations deteriorates during the firing cycle of porcelain.

PURPOSE

This study evaluated thermal cycling distortion of 3-unit porcelain fused to metal frameworks at different firing stages.

MATERIAL AND METHODS

A master model was designed to represent the 2 abutments of a 3-unit fixed partial denture replacing a missing mandibular molar. Standard techniques were used to fabricate 10 castings. Half of the copings were cast in a Ni-Cr alloy and the other half in a Pd-Cu alloy. Framework distortion was measured by means of inner fit changes, horizontal linear measurements of the framework length, and vertical fit changes of each retainer. Measurements were made (1) initially, (2) after degassing firing, and (3) after glaze firing. Differences between the firing cycles created distortion values of the retainers in 3 dimensions. Repeated measures ANOVA was used to analyze data statistically.

RESULTS

Measured differences between the 2 firing stages ranged from -47 to 81.7 micrometer. For both alloy groups, retainers showed increase in vertical gap that implied poorer vertical fit after porcelain application. Mean values of inner fit change recorded for porcelain application firing were higher in magnitude than the values of metal-conditioning firing. In addition, no statistically significant differences were found among alloy types.

CONCLUSIONS

A 3-dimensional distortion was observed both in Pd-Cu and Ni-Cr frameworks during porcelain firing cycle. The distortion seen after porcelain application firing was significantly greater than that seen after metal-conditioning firing. This result can be attributed to these factors, contamination of porcelain to the inner surface of metal coping and reduction in resilience of metal.

How well are complete dentures copied?

OBJECTIVE

To assess how accurately the same set of complete dentures could be copied by 12 different laboratories.

DESIGN

A prospective study.

SETTINGS

Completed by commercial laboratories used by GDPs in England (1996). Results were analysed and controlled by a university department.

SUBJECTS (MATERIALS) AND METHODS

The master set was constructed to include a midline diastema and a bilateral posterior crossbite. Twelve sets of silicone moulds of the master denture were prepared. GDPs selected commercial laboratories of their choice to receive the work.

MAIN OUTCOME MEASURES

All stages of the work were compared with the master dentures by returning them to a specially adapted articulator. Analysis was completed using preset criteria.

RESULTS

Only five of the returned copies were considered to have both good quality acrylic resin work and clear details of the teeth in wax. Only four cases reproduced the diastema. After processing, the occlusal vertical dimension had been increased in eight of the cases and the bilateral crossbite had been eliminated in all cases.

CONCLUSIONS

None of the final copy dentures were considered an accurate copy of the master dentures. There is considerable scope for further training of dental technicians in this important technique.

"Prosthetic condition" and patients' judgment of complete dentures

PURPOSE

This study introduces the concept "prosthetic condition", which combines the quality of complete dentures and residual alveolar ridges.

MATERIAL AND METHODS

A pilot study was performed to select quality criteria with an acceptable interobserver agreement. With these criteria, a clinical examination was performed to assess the quality of the existing complete dentures and the residual alveolar ridges of 397 complete denture wearers. During clinical examination, the interobserver agreement of the selected criteria was retested. The "prosthetic condition" was assessed by combining the scores for denture quality and quality of the residual alveolar ridges. Subsequently, participants' satisfaction with and complaints about their dentures were scored according to their answers to specific questions.

RESULTS

Logistic regression analysis demonstrated that no variable of the "prosthetic condition" proved to explain the denture satisfaction. Some variables of the "prosthetic condition" had a significant but not relevant correlation with some denture complaints.

CONCLUSIONS

More research is necessary to substantiate the concept "prosthetic condition" as an acceptable measure of professionally quality assessment of dentures and denture-bearing surfaces. However, in determining the treatment need of community-dwelling groups, this concept seems a more realistic measure than denture quality only.

The quality of impressions for crowns and bridges received at commercial dental laboratories

OBJECTIVE

To determine the quality of impressions for crown and bridge work made in general dental practice.

DESIGN AND SETTING

All impressions for crown and bridge work which had been sent to four commercial dental laboratories in the UK were assessed by two examiners, each laboratory being visited on two occasions.

MATERIALS AND METHODS

290 cases which had been received by the laboratories on the days of the visits were assessed for a number of factors related to quality. There was no selection or rejection--all impressions received were examined.

RESULTS

Flexible plastic trays were used for the majority of working impressions for crown and bridge work in general dental practice (72%), many had been re-used (> 13%), defects in the recording of the prepared teeth were common, and cross infection control was not routine.

CONCLUSIONS

Quality standards for impressions for crown and bridge work in general dental practice in the UK are a cause for concern if the sample of cases seen in this study is typical.

Resin-bonded fixed partial dentures. I. Proposed standardized criteria for evaluation

Since etched cast resin-bonded prostheses were introduced in 1980, many articles have been written about them. Most state that the reported clinical success of these bonded restorations has been based primarily on the longevity of the bonding. For a comprehensive evaluation, however, it is important not only to examine the bonding but also to evaluate the periodontal response. The proposed standard method provides a consistent and comprehensive evaluation of resin-bonded prostheses that is applicable for researchers and clinicians alike.

A new technique for determining the denture tooth bond

Defective bonds between resin teeth and denture base material remain a continuing source of failure. Findings from the limited number of studies on this topic are diminished by the numerous experimental approaches adopted. National and international standard specifications also adopt different methods of specimen preparation and physical straining. A critical appraisal of the various standards is carried out and a new procedure for determining the denture tooth to acrylic resin bond is described. A study using this technique found that physical modification and alginate contamination of the tooth had no significant effect on the bond strength. Ineffectual wax elimination was the main cause of failure.

Study of the acceptability of lateral interocclusal records by a modular articulator

Semiadjustable articulators are extensively used for routine restorative procedures. The instruments may be adjusted by lateral interocclusal records. However, it has been reported that semiadjustable articulators do not accept lateral interocclusal records from all patients. The Hanau modular system 194 semiadjustable articulator was introduced to develop occlusion with minimal error. The manufacturer recommends that the instrument should be adjusted by means of lateral interocclusal records. This study investigated the acceptability of lateral interocclusal records. Sixty lateral interocclusal records were made for 30 edentulous subjects, and the acceptability of the records was evaluated by use of the split-cast mounting procedure. Out of 60 lateral interocclusal records, 52 (87%) records were accepted by the articulator. A Z test was used for two proportions and was statistically significant (p < 0.05).

[Grinding precision and accuracy of the fit of Cerec-2 CAD/CIM inlays]

The grinding precision of one Cerec-1 (C1) and one Cerec-2 (C2) CAD/CIM unit each was evaluated using standardized inlay-like (mod) samples (n = 40) of Vita Cerec Mk II porcelain and Dicor MGC glass ceramic. Typical dimensions (B, E, F, H) of the sampleS were measured and the standard deviations (SD) analysed statistically using the F-test. SD of C2-machined sample dimensions were significantly lower using both Vita, B: p < 0.05; E: p < 0.001; F: p < 0.001; H: p < 0.001, and Dicor MGC, B: p < 0.05; E: p < 0.001; F: p < 0.001; H: p < 0.01, than those machined with C1, indicating a strong improvement of grinding precision of C2 compared to C1. Accuracy of fit to human molar cavities of mod inlays machined with C1 (n = 6) and C2 (n = 6) was evaluated using a scanning electron microscope with 100x magnification. The width of the interfacial luting gap was generally lower in C2 inlays (56 +/- 27 microns) than with C1 (84 +/- 38 microns). Significant differences (t-test) were seen in margin sections "cervical line angles above CEJ" (C1 = 124 +/- 44/C2 = 59 +/- 30 microns, p < 0.05), "cervical line angles at CEJ" (C1 = 109 +/- 55/C2 = 67 +/- 27 microns, p < 0.05) and "gingival margin above CEJ" (C1 = 81 +/- 32 microns/C2 = 31 +/- 18 microns, p < 0.05).

Disposable trays for complete denture construction: a dimensional study of a type frequently used in the UK and of its suitability for the edentulous population

This study compares the sizes of patients' edentulous arches with the shapes of a range of disposable stock trays from one manufacturer. In many dimensions there is considerable discrepancy between the two. It is concluded that, even with tray modification, it is almost impossible to obtain an accurate impression of the shape of the all-important sulcus regions. Such a conclusion emphasises the importance of obtaining further impressions in special trays which are modified appropriately.

A survey of the dissatisfied denture patient

A small but important group of complete denture wearers find great difficulty in adjusting to, and wearing, dentures. In the past, efforts have been made to identify a factor or group of factors which typify these patients so that the clinician, having recognised the factors, might modify the management approach accordingly. Most research has concentrated on one form of investigation. In this study a wide range of tests was applied to complete denture wearers attending for treatment at Cardiff or Leeds Dental School, including an exhaustive interview and questionnaire, clinical examination and a personality assessment. In the majority of cases technical errors in denture construction accounted for the presenting complaint. It was not possible to identify a factor or group of factors common to those patients who had suffered chronic denture problems.

Repeatability of a specially designed intraoral colorimeter

A specially modified Minolta CS-100 colorimeter with a DP-101 data processor was designed for intraoral use. To test the repeatability of the results obtained with this specially modified unit, five porcelain and five acrylic resin denture teeth were mounted in a fixed position in front of a fixed mounted meter. Three L*a*b* readings were taken per tooth and mean values were obtained after calibration as a baseline measurement. The readings were repeated on day 3 without recalibration and on day 8 after recalibration. The same-day repeatability showed delta E values < 0.4 in nine of the 10 samples. The day 3 repeatability showed delta E values < 0.4 in only 2 of the 10 samples. The day 8 results, after recalibration, showed delta E values > 0.4 in all of the samples, with a range of 0.57 to 2.75. In vivo testing was performed on five patients with delta E values that ranged from 1.1 to 32.1.

Complete denture prescription--an audit of performance

The quality of clinical records obtained during the various stages of complete denture construction was assessed in a survey conducted in five large dental laboratories in 1989. The most common fault in approximately half of 188 upper and 158 lower impressions was overextension in the labial and buccal sulci. Of the 87 occlusal records examined, the rims indicated the intended incisal relationship in about 50% of cases. The border of the eventual denture was defined by the technician rather than by the dentist in most instances. The post-dam was prescribed by the dentist in only 16% of the 50 trial dentures inspected. It is argued that a major cause of the lack of prescription is the level of the NHS fee, coupled with the fact that the laboratory expenses are deducted from that fee.