The influence of impression trays on the accuracy of stone casts poured from irreversible hydrocolloid impressions

HYDROXYAPATITE

AUGMENTATION

6.

created that cannot be used effectively for the support, retention, and stability of an intended prosthesis, little benefit is provided for the patient. Small variations in intended treatment can significantly increase success of the prosthesis (Fig. 13). Unfortunately, the relative ease of hydroxyapatite placement has led to its use in patients who do not require augmentation and augmentation in amounts and regions that are not conducive to improving denture success. A coordinated effort between the surgeon and the prosthodontist will usually result in treatment that provides the best potential foundation for a specific palient.

7.

8.

9.

IO. 11.

REFERENCES I.

2.

12.

(;riliiths ucc tor

JR: New hydroxylapatite ceramic materials: Potential hone induction and alveolar ridge augmentation. J ~RO~Tll~;l L&NT 53:109, 1985. Van Sickels JE: Review of surgical ridge augmentation procedures lor thr atrophied mandible. J ~RUi’rHKl’ L)ENT 51:s.

13. 14. 15.

1984. 3.

Ailing

Hydroxylapatite augmentation of edentulous ridges. &x1. 52:828, 1984. Kent JN. Quinn JH, Zide MF, Guerra LR, Boyne PJalveolar ridge with nonresorbable I\ugmentation of deficient hydroxylapatite alone or with autogenous cancellous bone. J Oral Maxillofac Surg 41:629, 1983. Kent .JN, Quinn JH, Zide MF, Finger IM, Jarcho M, Rothstein SS: Correction of alveolar ridge deficiencies with nonresorh~lble hydroxylapatite. J Am Dent Assoc 105:993, 1982.

J

4.

5.

(:(.

PROS

16.

I‘Hi;l’

Larsen HD, Finger IM, Guerra LR, Kent ,JN: Prosthodontic management of the hydroxylapatite denture patient: A prrliminary report. J PROSTHEI‘ DEN.1 49:461, 1983. Jarcho M, Bolen CH: Hydroxylaparite synrhesis and characterization in dense polycrystallinr form. J Mater SC] 11:2027, 1976. Jarcho M, Kay J, Gumaer KI, Doremus RH, Droheck HP: Tissue, cellular, subcellular events of a hone-ceramic hydroxylapatite interface. J Bioeng 1:79, 1977. Hickey JC, Zarh GA: Boucher’s Prosthodontic Treatment for Edentulous Patients. ed 8. St. I.ouis, 1980. The C\’ hlosby co. Winklrr S: Essentials for Complete Denture Prosthodontics. Philadelphia, 1979, WB Saunders Co. Heartwell Jr CM, Kahn AO: Syllabus of (:omplete Dentures, rd 2. Philadelphia, 1974, Lea & Fehiger. Jones JH, Mason DK: Oral Manifestation5 of Systemic Disease. Philadelphia, 1980, M’B Saunders Co Laney !VR. (iibilisco J:1: Diagnosis and ‘L‘reatmt~ in l’rtrsthodontics. Philadelphia. 1983. I,ra & ~ebi~er. Neil E: Full Denture Practice. NashLillr, 1932. pp 13-l;. hloses CH Physical ronsiderationa m imprrssion making. J ~‘ROTIIEI DENT 3:449, 1953. Permar D: Oral Embryology and Microscopic Anatom\. ed 5. Philadelphia. 1972, Lea & Febiger.

The influence of impression trays on the accuracy of stone casts poured from irreversible hydrocolloid impressions Arturo Louisiana

J. Mendez, State

D.D.S., M.Sc.*

University,

School

of Dentistry,

New

Orleans,

M

any factors can cause distortion in irreversible hydrocolloid impressions and subsequent inaccuracies in artificial stone casts. Dental materials or the dentist’s impression techniques are frequently blamed for discrepancies between oral tissues and stone casts. Howev-

Submitted in expanded form as a thesis in partial fulfillment of the requirements for the Master of Science degree at the Ohio State University, Columbus, Ohio. Presented in part at The Carl 0. Boucher Prosthodontic Conference, Columbus, Ohio. *.&ociate Professor, Department of Removable Prosthodonticq. THE

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La

er, little attention is given to the possibility of distortion being produced by using an inadequate impression tray. Different opinions exist concerning the selection of a suitable tray for irreversible hydrocolloid impressions. The objective of this study was to identify which of four commonly used impression trays helps make the most accurate irreversible hydrocolloid impression. This objective was achieved by determining the comparative accuracy of artificial stone casts that were obtained from irreversible hydrocolloid impressions made in trays with different characteristics. 383

Fig. 1. Master cast after being trimmed, polished, and treated with model-finishing soap.

were stock RimFig. 3. Four impression trays tested lock nonperforated; stock perforated; custom nonprriorated with spacer; and custom perforated with spacer Note that all impression trays have three acrylic resin stops at same locations,

Fig. 2. Fine, sharply defined pit was engraved on metal

plate and flattened surface of each metal crown.

LITERATURE

REVIEW

The literature is replete with discussions of the various types of impression trays used in making irreversible hydrocolloid impressions and the procedures used to improve or modify them. Emphasis has been given to the significant influence that the tray form has on the amount of impression distortion.’ Several authors have recommended the use of perforated impression trays. 2-6 Some researchers have suggested the use of Rim-lock (L. D. Caulk Co., Milford, Del.) nonperforated trays, while others prefer Rim-lock perforated trays.+’ The use of plain and perforated custom trays has also been advocated.*-” Recommendations to customize impression trays, to use adhesives, or to use other means of retention have also been made.3, s,I”-”

MATERIAL

AND

METHODS

A specially prepared stable cast (master cast) was used in this investigation. The master cast was made in

384

improved artificial stone (Silky Rock, Whip Mix Cot-pi Louisville, Ky.) with five cobalt-chromium crowns (Vitallium 2 alloy, Howmedica, Inc., Chicago, Ill.) and a square plate (Fig. 1). The crowns were designed with a flat plane. The plate and flat planes of the crowns were marked by means of a punch. The engraved marks consisted of fine and sharply defined pits (Fig. 2). Complete irreversible hydrocolloid impressions of the master cast were made using four different kinds of trays (Fig. 3): (1) stock Rim-lock nonperforated tray (NWC Caulk Rim-Lock impression tray, reguIar, Ull), (2) stock perforated tray (COE impression tray, extra long orthodontia style, XL5, COE Laboratories Inc.. Chicago, Ill.), (3) custom tray with spacer, nonperforated, and (4) custom tray with spacer, perforated. Perforations were at approximately 2.5 mm intervals and 2 mm in diameter. Although the placement of stops in stock trays is not a common clinical procedure, stops were used to minimize variables. The custom trays were made of autopolymerizing acrylic resin (Ontray, self-curing plastic, Teledyne Dental, Elk Grove Village, Ill.) by the adapting technique.” The two trays were fabricated with identical clearance (approximately 3 mm) and with stops. The proportions and temperatures used in mixing the materials were 57 ml water at 70” F to 19.5 gm powder for the irreversible hydrocolloid (Caulk Jeltrate, alginate impression material, Type II regular, normal set, batch No. 020378 3, L. D. Caulk Co.), and 58 ml water at 70” F to 200 gm powder for the artificial stone (Quickstone,

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IMPRESSION

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ACCURACY

Fig. 5. Monocular surface illuminator.

measuring

microscope

with

duplex

is fixed to microscope

stage

Fig. 4. Distances measured on casts. Top, a-b, b-c, c-a, and d-e (horizontal distances). Bottom, f-g (vertical distance).

buff, serial No. 0205824, Whip Mix Corp.). Doubledistilled water was used throughout. Because adhesives (Hold spray-on tray adhesive, Teledyne Dental) for irreversible hydrocolloid impressions are extensively used, they were applied to both nonperforated impression trays in every instance. Ten impressions were made with each type of tray. They were coded as follows: Stock Rim-lock nonperforated Stock perforated Custom nonperforated Custom perforated

A B c D

The pouring procedure was started immediately after the impression was separated from the master cast using the two-stage technique.” The artificial stone was mechanically spatulated (Whip Mix power mixer, Whip Mix Corp.), the plastic bowl was vibrated, and the stone mix was then vibrated into the impression. The mixing, vibrating, pouring, and setting procedures were standardized and strictly controlled with a timer. Once recovered, the stone casts were examined for accuracy and, if acceptable, were code marked for future identification.

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Fig. 6. Cast to be measured with

sticky wax.

The distances between the marks on the casts were measured for comparison. Fig. 4 shows the distances that were measured by means of a monocular measuring microscope (Universal Toolmaker microscope, Model UWM, Leitz Wetzlar, W. Germany), which allowed readings in the 0.0001 inch range (Figs. 5 and 6). The five separate distances to be evaluated on each cast were measured by the same operator one time (Fig. 4). After all 40 casts were measured, the same distances were measured on the master cast in exactly the same manner, except that they were repeated three times.

385

Table I. Descriptive Casts Master A Master A Master A Master A Master A Master B Master B Master B Master B Master B Master C Master C Master C Master C Master C Master D Master D Master D Master D Master D *Value

for master

statistics and t tests for casts comparisons -___Distance

Mean*

a-b a-b b-c b-c c-a c-a d-e d-t,

2.0541

f-g f-g a-b a-b b-c b-c c-a c-a d-e d-e

0.861

Standard error

t value*

2.0536-2.0581

.OOlO

- 00044

2.1993 1.8364

2.1953-2.2004

.0030

L.OOO5I

1.8376

1.8371-1.8385

.0012

-c.OOOlh

1.4390 1.4393

1.4381-1.4411

.0003

-i-.00028

0.866 2.0541

0.859-0.884

,005

2.00234

1.069

2.0539 2.1963

2.0520-2.0566

.0002

i .00041

0.234

2.1979

2.1959-2.2002

.0016

t.00047

l.h47

1.8363 1.4390 1.4386 0.861

1.8348-1.8377

.OOOl

r.00028

0.180

1.4373-1.4400

.0004

i_ .00035

0.594

0.869 2.0541

0.856-0.885

,008

-t .(I0335

1.200

2.0545

2.0535-2.0556

.0004

t.00022

0.891

2.1963 2.2005

2.1971-2.2019

.0042

3: .00051

4.209/i

1.8373 1.4390

1.8365-1.8383

-0009

rt.00019

2.3335

d-e

1.4390

1.4372-1.4403

.oooo

i.00032

0.000

f-g

0.861 0.868 2.0541

0.858-0.886

,007

it 00269

1.310

2.0533

2.0515-2.0564

.0008

r?.ooo44

0,927

2.1963 2.1987

2.1923-2.2021

.0024

L.00111

1.085

1.8364 1.8375

1.8346-1.8395

.0011

+.00051

1.095

1.4372-1.4422

.0004

~.00051

0.393

0.856-0.890

,011

k.00379

f-g f-g a-b a-b b-c b-c c-a c-a d-e

f-g

a-b a-b b-c b-c c-a c-a d-e d-e f-g f-g cast represents

2.0551

1 131

2.1963

1.8364

1.8364

1.4390 1.4394 0.861 0.872

mean of thrrr

-

tletrrminations

for each distance.

All calculations were performed, and values for the measured distances were recorded. RESULTS Descriptive statistics were computed for the master cast and four type casts based on the measurements for each distance (Table I). The comparative t distribution method (t test) was used to determine whether there were significant differences between each type of cast and master cast. A separate analysis was performed for each of the five measurements. 386

Mean differencet

Range

The null hypothesis tested was that there would be no significant differences between any of the type casts and master cast for any of the measurements. The detailed results are presented in Table 1. DISCUSSION The results of this study show that all the impressionsmade with the tested trays presented some kind of distortion. The mean values revealed 8hha except for the impressions made with the stock perforated tray (B) , ail the impressions had a tendency to be oversized. Three of SEPTEMBER

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IMPRESSION

TRAYS

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CAST

ACCURACY

the five cast B means were smaller than the master cast means (Table I). Four t values reflected statistical significance (Table I). Based on clinical observations, it seems that the posterior border of a maxillary impression (including the distobuccal region) is prone to distortion. Undercuts around the maxillary tuberosities and the seal of the impression in that region may provoke such distortion. This type of distortion was probably one factor responsible for the statistically significant values in the measurements of distance c-u. Failure of the nonperforated type of trays (A and C) to adequately hold the irreversible hydrocolloid in the regions mentioned above could have been another reason for distortion. According to the t test, the overall behavior of the stock perforated tray (B) was the most satisfactory (Table I). However, three of the five range values were relatively wide, and irregular mean values resulted as compared with the master cast values. In general, the calculated mean differences of the stock perforated tray (B) were the smallest of all. The facial flange on this tray was shorter than on the other trays. For this reason, a slightly underextended impression of that region always resulted. Irreversible hydrocolloid did not flow to the facial undercut present on the master cast, and this made withdrawal of the impressions from the master cast easier. This could have been a favorable factor for the impressions made with the stock perforated tray, since the shear stress was probably reduced in that region. Even though the custom perforated tray (0) demonstrated satisfactory results according to the t test (Table I), a wide range of measurements, irregularity of the mean values, and comparatively high mean differences indicate that the use of this type of tray does not guarantee predictable results. The use of the Rim-lock nonperforated tray (A) demonstrated fair results, as the t test showed (Table I). Two of five distances were statistically significant. An overall analysis of the ranges shows that they had a tendency to be comparatively narrow. All five mean values of the measured distances were higher than the mean values of the master cast; and in general, the mean difference values were high. According to the t test (Table I), the custom nonperforated tray (C) demonstrated similar but less satisfactory results than those of the Rim-lock nonperforated tray (A). In general, the ranges of measurements of the custom nonperforated tray (C) were moderately narrow. The mean values of four of the distances measured were larger than the means of the same distances on the master cast; the mean values for the fifth distance were identical. In general, the calculated mean differences were the second lowest. The reproducibility of the palatal region (around THE

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point g, Fig. 4) is critical when making an irreversible hydrocolloid impression for the construction of a prosthesis. Any distortion that occurs in this region will affect the accuracy of fitting major connectors or denture bases. These facts demonstrated the necessity of comparing measurements of distance j-g to evaluate changes that occur in the impressions made with different types of trays. The t test showed that the means for distancef-g measured on any of the cast series were not significantly different from the mean for distance f-g on the master cast (Table I). Apparently, the impression tray that presented the least degree of distortion in the palatal region was the Rim-lock nonperforated tray (A) followed by the stock perforated tray (B) (Table I). The two stock impression trays used in this study were used with no modification other than the placement of occlusal stops. It would be interesting to test the accuracy of these types of trays modified as recommended by several authors.“, “, ‘L “a I8 A second proposal for future evaluation would be the behavior of nonperforated impression trays without adhesive for irreversible hydrocolloid. The four t values that were statistically significant (Table I) were not thought to be clinically significant. Mean differences of 0.015 inch or greater were considered to have clinical significance. SUMMARY

AND

CONCLUSIONS

An investigation was conducted to determine which of four commonly used impression trays yields the best results when making irreversible hydrocolloid impressions. This objective was achieved by evaluating the comparative accuracy of stone casts obtained from irreversible hydrocolloid impressions made with trays of different characteristics. The following conclusions are drawn from this study. 1. Some kind of distortion can be expected in irreversible hydrocolloid impressions with the use of any of the tested impression trays. 2. The perforated trays (B and D) reproduce more accurately the distances along the length and the width of the arch than the nonperforated trays (A and C). 3. The depth of the palatal vault (distance f-g) is reproduced most accurately by the Rim-lock nonperforated tray (A) followed closely by the stock perforated (B) and the custom nonperforated (C) trays. 4. Under the conditions of this study, all the impressions had a tendency to be oversized except the impressions made with the stock perforated tray (B). Those impressions were slightly undersized for all but two measured distances. 5. Clinically significant inaccuracies produced by any of the four tested impression trays were not found in this study. 387

MENDEZ

1 wish to acknowledge Dr. I). W. Foreman, Ohio State University, College of Dentistry, Columbus. Ohio, for his assistance in the statistical analysis of this research project.

9.

Johnson

1,N: Alginate impression materials. J C:an Dcnc Asw 1975. Einlrldt II: ‘l’he ale;inaw impression. Quintrssewc 1111 4:i7,

41:4?, IO.

1973. II.

REFERENCES 1. 3-.

hliwhell JV, Damele JJ: Influence of tray design upon elastic impression materials. J PKOSTHCT Dl;~‘r 23:151, 1970. Skinnrr LW. Cooper EN, Beck FE, Reversible and irreversible hydrocolloid impression marerials. J Am Dent :\~soc 40: 196,

4.

5 6.

7.

8.

18. 14.

1950.

3.

12.

Skinner EW, (Carlisle FB: The use of alginate impression materials in the Sears hydrocolloid impression technique. J P~osr~~tr Dl:w 6:405, 1956. liear~wrll Jr CM. hlodjeski PJ, hlullins Jr EE, S~rader KII: (:omparison of impressions made in perforated and nonperforawd Rim-lock trays. ,J PRosr!ler DE~V I 27:494, 1972. Phillips RW: Skinner’s Science of Denral Mawrials, cd 7. Philadrlphia. 1971. WB Saunders Co, pp 124-126. Bouchcr (:O. Hickey JC, Zarb GA: Prosrhodontic Treatmem for I~dcnrulous Palicnts. ed 7. St. Louis. 1975, The CV hlosb) c:o. t:usayam~ 1’. Nak.lzno hl: The designs of stock trays and [he rrwnrion of irre~rrsible hydrocolloid impressions. J PROS.TIIE.I DEYI 21:) 36. I960. Hollcnberk Ghl: :\ study of the physical properties of elastic imprcasion marerials (The linear and over-all accuracy of rrvcrsiblc and irreversible hydrocolloids) Part IV. J South Calif State Dent :\ssoc 3b40.1, 1963.

15.

16. 17.

Henderson L), Strllel VI,: hlrC:racken’s Removable Pa&l Prosthudontics, ed 5. St. Louis, 1977, Thr CV hlosby C:o Rudd I(L), Dunn BW: ~\ccuratc removahlr parri,tl drnrurcs. J PKOS.~H~I D)EN.I. 18:559, 1967. !Vilscm HJ, Smith DC: The honding of alginatr impression ma~crials to impression trays. Br I)cnt J 115:X I, 1963. ,~~kinsnn IiF‘, Gill F-II. Shepherd RW: Some nntcs on ,rlqinaw imprtssion material. ~\ust Dent J 3:184, 195X. Sandini MS, De Rbreu D: Inlluencia do Cpo de moldcira na reprodutibilidadc de mod&s de gesso, obtidns a partir dr moldes de alginato. Estomatol Cuhura 9:109. 1975. Rudd KD, ~lorrow Rhl, Bange AA: :‘\ccuraw casts. J PROS.I~III..I DES-~ 21:545. 1969. Jordan I.<;- /\Iginarc impression m,rtcrials. J ;\m Drnt Asw 32:985,

18.

1945.

Rudd KU, A~lorrow Rhl, Strunk RR: .Arcura\r sions. ,J PRO.I.III-I DEN.I. 22:294, 1961).

al+nale

rmpres-

Cephalometrically programmed adjustable plane: A new concept in occlusal plane orientation for . complete-denture patients Brian D. Monteith, Medical

University

M.Ch.D.*

of Southern

Africa, Faculty of Dentistry,

1t

is unfortunate that no precise, scientific methoa exists for determining the level of the occlusal plane in edentulous patients. Hickey and Zarb,’ express this opinion, but find some assurance in the existence of certain basic principles that have proved to be clinically successful and that may be used to help achieve this objective. Prominent among the principles is the method of orienting the occlusal plane parallel to the ala-tragus or Camper’s line. This is not a new concept (Spratley2 cites a pre-1920 textbook by Fripp as having recommended

*Professor

388

and liead,

Department

of Prosthodontics.

Medunsa,

Republic

of South Africa

its use), and its currency has not diminished. Of eight modern texts consulted,‘,3-9 only one’ makes no mention of its usefulness. In view of such widespread recommendation, it is surprising how much vagueness exists as to the exact nature of the ala-tragus line. Boucher” defines it as, “The line running from the inferior border of the ala of the nose to the superior border of the tragus of the ear.” However, of the seven texts that propound its use, only one provides definition, and it cites Boucher’s definition.5 Two texts’, ’ recommend the concept without defining or illustrating it, while three3, 4,’ provide only pictorial representation. The latter are of immediate concern, for in each illustration, Camper’s line is clearly depicted as SEPTEMBER

1985

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