teaching an abbreviated impression technique for complete dentures in an

7/29/2019 Teaching an Abbreviated Impression Technique for Complete Dentures in An

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Most US dental schools teach the fabrication ofcomplete dentures with a final (secondary) impressionin a border-molded custom tray.1 Although materialsmay vary, the principles are similar. Despite the unifor-mity of training, a substantial percentage of generalpractitioners appear to abandon what they have beentaught and after graduation elect a simpler method formaking complete denture impressions.2-4

Until recently, the University of Connecticut taughta selective pressure technique for complete denturefinal impressions. A custom tray was border molded

with modeling compound, and a final impression wasmade with a low-viscosity condensation siliconeimpression material. Students then were instructed tofabricate a record base on the master cast by using alight-polymerized resin. Although this method wasmoderately successful, several difficulties were routine-ly encountered.

First, the process of border molding was a difficulttechnique to master for students with limited expo-sure. With a limited number of complete denturepatients available, students rarely had the opportunityto become proficient at this procedure. Faculty fre-quently had to intercede in the process to produceadequate final impressions. Second, the number of vis-its necessary to obtain an acceptable impression wasexcessive. Three to 4 visits were routinely needed tocomplete the examination, treatment plan, and prelim-inary and final impressions. Third, despite much effortat the border molding and final impression stage,many dentures were found to be overextended at thetime of delivery. And fourth, students had difficultyfabricating well-fitting record bases with light-polymerized resin. Palatal pull away, brittleness andfrequent fracture, difficulty in getting baseplate wax toadhere, and the inherent poor wettability of the light-polymerized materials combined to make their usesomewhat problematic.5 Auto-PMMA record bases

were not an option because of a decision made by the

Teaching an abbreviated impression technique for complete dentures in anundergraduate dental curriculum

Jacqueline P. Duncan, DMD, MDSc,a and Thomas D. Taylor, DDS, MSDb

School of Dental Medicine, University of Connecticut, Farmington, Conn.

Statement of problem. Traditional methods for teaching complete denture fabrication are time-consuming, difficult to master, and not used by many general practitioners.Purpose. This study compared the efficacy of traditional denture fabrication techniques with a moreabbreviated method in a dental school setting.Material and methods.A retrospective record review of 80 completely edentulous patients treated bypredoctoral dental students was completed. Forty patients were treated with traditional denture tech-niques; the other 40 patients were treated with an abbreviated method. The data abstracted included thenumber of visits to completion and the number of postinsertion visits and relines required within the first3 months after delivery. A Wilcoxon rank sum test was performed to determine statistical significancebetween the groups with regard to number of visits for fabrication and postinsertion adjustments. A testfor a difference in proportions by using the normal approximation to the binomial distribution was per-formed for statistical analysis of the incidence of relines.Results. The abbreviated denture technique resulted in a statistically significant difference in the numberof visits for fabrication (P


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University of Connecticut concerning the possibility ofhigh levels of monomer released in the student labora-tories and potential related health concerns ofoccupational safety.

Because of delays and additional visits needed fordenture fabrication, problematic materials being used,and the realization that the average general practitioneris unlikely to use a complicated technique for complete

THE JOURNAL OF PROSTHETIC DENTISTRY DUNCAN AND TAYLOR

122 VOLUME 85 NUMBER 2

denture final impressions, it was decided that the tech-nique taught to dental students would be modified.

Students now are taught to make heat-processedacrylic resin denture bases directly on casts obtainedfrom overextended irreversible hydrocolloid impres-sions made in stock trays. This technique requires ahigh-quality irreversible hydrocolloid impression withoverextension in all areas. Border extensions for the

Table I. Comparison between the number of visits required with the traditional denture impression technique (n = 40patients) and an abbreviated technique (n = 40 patients)

Number of visits to Postinsertion visits during Number of visits to complete Postinsertion visits duringcomplete denture fabrication* first 3 months after delivery denture fabrication* first 3 months after delivery

Traditional technique Traditional technique Abbreviated technique Abbreviated technique

6 3 4 0

7 1 4 27 5 4 2

7 3 5 2

7 3 5 3

7 1 5 2

7 1 5 3

7 4 5 3

7 2 5 2

7 2 5 4

8 1 5 2

8 1 5 2

8 3 6 2

8 2 6 2

8 5 6 1

8 8 6 38 1 6 0

9 2 6 4

9 3 6 1

9 2 6 1

9 3 6 0

9 3 6 5

9 3 6 2

9 6 7 2

9 1 7 1

9 3 7 3

9 4 7 4

9 1 7 0

10 7 7 0

10 6 7 110 3 7 2

10 3 7 7

10 12 8 2

10 1 8 2

11 3 9 1

11 5 9 2

11 5 9 5

12 2 9 4

13 5 11 1

14 0 11 1

Mean 8.90 3.23 6.5 2.15

Median 9** 3*** 6** 2***

*Numbers listed do not include postinsertion visits.

**Statistically significant P


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denture bases are determined by marking the cast atthe point where the alveolar process begins to turninto vestibule. The posterior palatal seal is arbitrarilymarked at the fovea palatinae and carved into the cast.The student determines the border extensions withfaculty assistance, carves the posterior palatal seal area,

and then adapts 2 thicknesses of baseplate wax to thecast, trimming it precisely to the drawn lines. After thepattern is processed, the student places wax occlusionrims and fabricates mounting casts poured into thedenture bases modified with appropriate block out.

At the second visit, the student and patient areready for jaw relation records, tooth selection, andmounting of the casts. The first step is to evaluateretention and stability of the processed bases. This taskis accomplished with pressure-indicating paste. Tissueadaptation and border extensions are evaluated andadjusted at this stage. This provides the student withan early determination of the stability and retention of

the final dentures. If retention or stability is found tobe lacking, plans are made to include a laboratoryreline at delivery.

After maxillomandibular relations and esthetic try-in visits are completed, the teeth are processed to thedenture base. It has been documented that secondaryprocessing of the denture base does not cause any sig-nificant dimensional changes in the base.6,7

The goals of this technique are to reduce thenumber of visits and improve the quality of recordbases without compromising the quality of the finaldentures. The purpose of this retrospective study

was to compare the efficacy of the traditional versus

abbreviated techniques for fabricating complete den-tures in a dental school setting by comparing thefollowing parameters: (1) number of visits neededfor denture fabrication, (2) number of postinsertion

visits, and (3) frequency of additive corrections(reline) required by the traditional and abbreviatedtechniques.

MATERIAL AND METHODS

The records of 80 arbitrarily selected, completelyedentulous patients treated by predoctoral students

were reviewed. These patients were divided equallybetween the traditional technique and abbreviatedtechnique for denture fabrication. The number of vis-its to completion and the number of postinsertion

visits and relines required within the first 3 monthsafter delivery were recorded.

A Wilcoxon rank sum test was used to analyze thenumber of visits and number of postinsertion visits. Atest for the difference in proportions by using the nor-mal approximation to the binomial distribution wasapplied to analyze the statistical significance of theoccurrence of relines between the 2 groups. Results

were considered significant at the P


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when a students complete denture experience isminimal. Students and practitioners should be com-fortable making and recognizing high-qualityirreversible hydrocolloid impressions. And third,the need for a clinical remount is virtually eliminat-ed at the time of denture delivery. Mounting casts

are made directly into the processed bases. Thesecasts remain mounted on the articulator after cen-tric relation has been verified at the esthetic try-inappointment. After final processing of the dentureteeth to the denture base, the laboratory technicianis able to place the dentures back on the articulatorsecurely and accurately. The technician and/or stu-dent then are able to make final postprocessingadjustments to the occlusion.

The apparent reduction in the number of postin-sertion visits also appears to be an advantage of thismodified technique. However, there are inherentdifficulties in using postinsertion visits as a com-

pletely valid indicator of denture success. It has beenwell documented that the success of dentures reliesheavily on patient acceptance rather than on theabsolute quality of the prosthesis.8-10 This study didnot examine patient satisfaction or acceptance of thedelivered dentures. In addition, routine postinser-tion appointments are to be scheduled for allpatients, which require the patient to return at leastonce during the 3 months after denture delivery. Ascan be seen in Table I, this did not always occur.Unfortunately, compliance for these appointmentscan be enforced only within practical limits. Onemust assume that patients having difficulty will

return for adjustments.No change in the incidence of relines between

the 2 groups is also a positive indicator of theacceptability of the abbreviated technique. A defi-nite trend was found in the treatment planning ofrelines. One instructor, of 9 available, was found tohave recommended at least a third of the relinesperformed between the 2 groups. This tendencylikely is related to the subjective nature of completedenture evaluation and the personal preference ofthe instructor.

Although this technique has proven to be accept-able in this study, attention to the denture baseborders is obviously critical. With the traditionaltechnique, dentures on occasion were returnedfrom the laboratory with knife-edge, overtrimmedborders. This occurred although the vestibule hadbeen border molded and waxed to full contour onthe master cast. With the abbreviated technique,there is potential for student error as well as labora-tory error. If the thickness of the wax pattern for thedenture base is not maintained at the denture bor-

ders, the borders will likely be insufficient. At theUniversity of Connecticut, stricter adherence todetail has been emphasized to faculty, students, andlaboratory technicians, and the importance of aneffective quality control mechanism has been reiter-ated. Anecdotally, it has been found that it is better

to err on the side of overextension of the initial den-ture base wax pattern because it is easier to reducethe borders than to add to them.

CONCLUSIONS

The following conclusions can be drawn from thisstudy:

1. A 1-step irreversible hydrocolloid impression ina stock tray, in place of the traditional final impres-sion in a border-molded custom tray, significantlydecreased the number of visits required to fabricatecomplete dentures in a student clinic (6.5 vs 8.9 vis-its, respectively) (P


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Reprint requests to:DRJACQUELINE P. DUNCAN

DEPARTMENT OF PROSTHODONTICS

UCONN HEALTH CENTERFARMINGTON, CT 06030-1615

FAX: (860)679-1370E-MAIL: [email protected]

Copyright 2001 by The Editorial Council of The Journal of ProstheticDentistry.

0022-3913/2001/$35.00 + 0. 10/1/113699

doi:10.1067/mpr.2001.113699

DUNCAN AND TAYLOR THE JOURNAL OF PROSTHETIC DENTISTRY

FEBRUARY 2001 125

Fatigue behavior of the zinc-phosphate cement layer

Yamashita J, Takakuda K, Shiozawa I, Nagasawa M, Miyairi H.

Int J Prosthodont2000;13:321-6.

Purpose. This study examined the strain responses and ultimate tensile strength of cantileverfixed prostheses cemented onto brass dies with a zinc-phosphate luting agent.Material and methods.

Fifty-six 7.6-degreetapered brass dies were manufactured. Twenty-eight had 2 grooves posi-tioned bilaterally, and 28 were manufactured without grooves. Standardized cantilever fixedpartial dentures (FPDs) were fabricated for each die with handles at the center of the occlusalsurface for tensile testing purposes. The FPDs were composed of 12% Au-Pd-Ag alloy (CastwellMC, GC). Four single element strain gauges were placed onto the marginal portion of eachretainer parallel to the long axis of the die. The FPDs were cemented onto each die under fingerpressure for 1 minute with zinc-phosphate luting agent (Elite 100, GC). Each cemented speci-men was allowed to stabilize for 10 minutes before removal of excess luting agent. All specimens

were stored for 24 hours at 37C in a 99% humidity environment. The nongrooved specimenswere divided into 3 subgroups. Two of the subgroups comprised 10 specimens each, and thethird subgroup comprised 8 specimens. The grooved specimens were similarly divided. With acustom-designed fatigue testing machine, repetitive loads of 50 N were applied to 20 specimens(10 grooved and 10 nongrooved). Total loading cycles equaled 5.5 105. All fatigue tests werecompleted in 37C water, and testing was completed in 153 hours. Twenty specimens (10grooved, 10 nongrooved) also were subjected to 100 N loads over the same period with the sametotal loading cycles. The remaining 16 specimens served as controls and were stored in 37C

water for 153 hours. Before repetitive loading began and after every 0.5 105 cycles, strainchange was observed as the applied load increased. After fatigue testing, the ultimate tensilestrength of each specimen was measured by using a crosshead speed of 0.5 mm/min. A 2-way

analysis of variance (

=.05) was used to compare tensile strength among the groups.Results. Strain responses were similar at every strain measurement for grooved and nongroovedspecimens using the 50-N load. By using the 100-N load during fatigue testing, no difference instrain responses was observed for the grooved specimens; however, strain responses for the non-grooved specimens exhibited differences before and after repetitive loading. No significantdifferences were observed in ultimate tensile strength among the specimens after fatigue testing.Conclusion.After repetitive loading, no fatigue fracture was observed in the zinc-phosphate lut-ing agent. Stress transmission within the zinc-phosphate luting agent may be improved afterrepetitive loading.8 References. DL Dixon

Noteworthy Abstracts

of theCurrent Literature

teaching an abbreviated impression technique for complete dentures in an

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