Comparison of impression materials for direct multi-implant impressions

Although true “passive fit” of multi-implant–sup-ported prostheses to their intraoral implant abutmentsdoes not seem attainable,1-6 it remains unclear whatdegree of implant prosthesis misfit will lead to compli-cations. For this reason, meticulous and accurateimplant prosthodontic procedures are recommended asa means to attain the best possible fit.5 The implant castis the foundation on which the prosthesis is indirectly

fabricated. The use of the implant cast as a reference forextraoral implant framework fit facilitates the clinician’sevaluation of fit.

Strategies to achieve fit may be completed on themaster cast before the patient’s clinical appointment.Several strategies have been suggested to reduce thedistortion of the implant framework, namely, laserwelding of titanium implant framework,7,8 or use ofelectric discharge machining of the gold cylinders ofthe implant framework to the abutment replicas.9-11

Many intraoral techniques used to improve frameworkfit may also be used on the implant cast, given adequateaccuracy.5 Although absolute accuracy of the implantcast does not appear to be attainable at this time,3,12-14

it has been suggested that the distortion of the implant

Comparison of impression materials for direct multi-implant impressions

Alvin G. Wee, BDS, MSa

College of Dentistry, The Ohio State University, Columbus, Ohio

Statement of problem. Given that meticulous implant prosthodontic procedures are recommended toobtain the best possible intraoral fit, impression materials that are suitable for use with a direct impressiontechnique warrant further investigation.Purpose. This in vitro study compared the amount of torque required to rotate a square impression cop-ing in an impression and evaluated the accuracy of solid implant casts fabricated from different impressionmaterials.Material and methods. Two direct transfer implant impressions were made using 8 impression materials;the torque required to rotate an impression coping in the impressions was calculated. Ten direct transferimplant impressions were made from the master model and poured in a die stone (Resin Rock) for 3 of the8 initial impression material groups. Linear distances between steel balls placed on each abutment replicawere measured with a traveling microscope to determine distortion in the impression procedure for eachgroup. Data were analyzed (P=.05) with ANOVA and Ryan-Einot-Gabriel-Welsch multiple range test forpost hoc. Results. With a 1-way ANOVA, average torque values among the material groups differed significantly(P=.001). Polyether (medium consistency) was found to produce the highest overall torque values, followedby addition silicone (high consistency), and then polysulfide (medium consistency). Statistically significantdifference was also found among the 3 material groups’ mean absolute cast error using a 1-way ANOVA(P=.0086). Implant casts made from polyether (medium) or addition silicone (high) impressions were sig-nificantly more accurate than casts made from polysulfide medium impressions.Conclusion. On the basis of the results of this study, the use of either polyether (medium) or addition sili-cone (high) impression is recommended for direct implant impressions. (J Prosthet Dent 2000;83:323-31.)

This project was supported in part by funds from The Ohio State Uni-versity College of Dentistry and presented in part at the 1999International Association of Dental Research Annual Session as afinalist for the 1999 Arthur R. Frechette Prosthodontic ResearchAward competition.

aAssistant Professor, Section of Restorative Dentistry, Prosthodonticsand Endodontics.

MARCH 2000 THE JOURNAL OF PROSTHETIC DENTISTRY 323

CLINICAL IMPLICATIONS

Use of medium consistency polyether and high consistency addition silicones is recom-mended to make a direct implant impression, depending on the amount of hard tissueundercuts present in the arch. In this study, polyether minimized the chance of acci-dental displacement of the direct impression coping when the abutment replicas weretightened. Addition silicone in a partial edentulous arch facilitates the removal of theimpression tray when hard tissue undercuts are present, although care must be takento avoid accidental rotation of the impression coping. A double impression techniqueusing a lower consistency addition silicone wash did not appear to present any advan-tage for use in direct implant impressions.

cast be minimized during its fabrication to improve fit.5The accuracy of the implant cast depends on the typeof impression material,15 the implant impression tech-nique,12,15-22 die material accuracy,14 and the implantmaster cast technique.12,13

A number of implant impression techniques havebeen described,23,24 but the more common include theindirect, direct, and direct-splinted. The main purposeof a multi-implant impression is to record and transferthe relationship between implant abutments orimplants and to reproduce this relationship as accurate-ly as possible. Implant impressions also serve a sec-ondary but important purpose of recording soft tissuemorphology. Most research indicates that the indirectimpression technique produces a greater mean distor-tion than the direct-splinted and the direct tech-niques.12,17,18,20,21,25 When comparing the direct anddirect-splinted techniques, conflicting results have beenreported regarding their accuracy. However, most ofthe studies found the direct technique to be more accu-rate than the direct-splinted technique.17,21,25,26

When using the direct implant impression tech-nique, the impression material must fulfill 2 require-ments: (1) rigidity to hold the direct impression copingand to prevent accidental displacement of the copingwhen an abutment is connected, and (2) minimal posi-tional distortion between abutment replicas as com-pared with their intraoral implant abutments. Regard-ing rigidity, the amount of torque required to rotate adirect implant impression coping in different implantimpression materials has not been thoroughly investi-gated to date and can be considered an important char-acteristic of direct impression technique for implantimpressions. Liou et al27 reported that indirect impres-sion copings did not return to their original positionwhen replaced in either polyether or addition silicones.It is assumed that the same is true when direct impres-

sion copings are accidentally rotated. Therefore, thepractitioner may be less likely to accidentally displacethe impression coping by using a more rigid impressionmaterial. This rigidity can be indirectly measured byevaluating the amount of torque required to rotate theimpression coping in the impression. Regarding posi-tional distortion, Barrett et al15 did not find any signif-icant difference between the accuracy of direct implantimpressions that were made from polyether and thosemade from addition silicones. In addition, the implantimpression technique groups, namely, direct, direct-splinted, and indirect, did not vary significantly in accu-racy, a finding that is contrary to the results of otherstudies.16,20-22,25

Even though several impression materials are manu-factured with a range of consistency, comprehensivecomparison has been made to document the rigidityand accuracy of these materials/consistency types, asrequired for the direct implant impression technique.Because of a low strain in compression (flexibility) andfavorable Shore A hardness, polyether has been recom-mended as an impression material for edentulous, mul-tiple implant-retained restorations.12,18-22,25,28-31 Theuse of addition silicones has also been recommended asa material for direct implant impressions.15,16,32

Although polyether and addition silicones havereceived more attention in research and practice, thepotential variance within and/or between impressionmaterial groups warrants a complete evaluation.

The purposes of this study were to: (1) evaluate theamount of torque required to rotate a direct implantimpression coping in various impression materials whentightening the abutment replica, and (2) compare theaccuracy of solid implant casts produced from thedirect implant impression procedure with variousimpression materials.

MATERIAL AND METHODS

This in vitro study compared the torque required torotate direct square impression copings in 8 impressionmaterial groups. Those material groups that producedtorque values detectable by a torque-measuring unitwere then compared for implant cast accuracy. Animplant master model (Anderson Precision Machining,Inc, Iowa City, Iowa) was milled from a solid alu-minum block. Five stainless steel abutment replicas(DCA 174, Nobel Biocare USA Inc, Chicago, Ill.)were cemented symmetrically in an arch with an adhe-sive resin cement (Panavia 21, Dental Adhesive,Kuraray Dental J, Morita, Tustin, Calif.). Abutmentreplicas were spaced 12 mm apart and labeled A to E(Fig. 1).

Ten similar impression trays were fabricated fromlight-polymerized resin (Triad, Dentsply, York, Pa.),and 10 sets of 5 direct square impression copings (DCB026, Nobel Biocare USA Inc) were distributed ran-

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324 VOLUME 83 NUMBER 3

Fig. 1. Aluminum implant master model milled out of alu-minum block. Abutment replicas are labeled A to E from leftto right.

domly. Direct impression copings were hand-tightenedto the master model by guide pins. Adhesive was paint-ed on the impression trays 24 hours before impressionswere made.33 Impressions were made on the mastermodel and allowed to set for twice as long as the man-ufacturers’ recommended setting times.34

Torque displacement

Sixteen impressions were made of the master model,namely, 2 impressions for each of the 8 impressionmaterials/combinations evaluated (Table I, italicizedand bold-highlighted materials). Stainless steel abut-ment replicas (DCA 174, Nobel Biocare USA Inc)were secured carefully to the direct impression copingswith guide pins. Impressions were allowed to set for 30minutes to simulate laboratory pouring time fromimpression taking. A Compudriver device (Consolidat-

ed Device Inc, City of Industry, Calif.) was attached toan adapter one-quarter drive (Craftsman, HoffmanEstate, Ill.) and a 5-6 bit slotted 3⁄8-in. driver (Crafts-man) (Fig. 2). The 5-6 bit slotted driver was placed onthe slotted guide pin of the impression coping to betested, then the driver was rotated clockwise until theimpression coping was displaced once in the impressioncomplex (Fig. 3). The Compudrive device recorded theamount of torque required to rotate the coping in theimpression through the slotted guide pin–abutmentanalog complex. Torque values for 5 impression cop-ings for each of the 16 impressions were measured.

Statistical analyses of torque data were performedwith SAS software (version 6.12, SAS Institute Inc,Cary, N.C.).35 Repeated measures analysis of variance(ANOVA) (α=.05) was used to evaluate torque valueswithin and among impression material groups, as well

WEE THE JOURNAL OF PROSTHETIC DENTISTRY

MARCH 2000 325

Fig. 2. Compudriver with attachment and slotted drive. Fig. 3. Slotted drive of Compudriver rotating square impres-sion coping in implant impression.

Table I. Impression materials evaluated*

Batch Strain in Shore A AccuracyMaterial Name and company Consistency number compression48 hardness48 (24 h)48

Polyethers Impregum F (Premier Dental Products Co, Medium 28621 2%-3% 35-60 –0.24%Norristown, Pa.) High 28621 3% 40-50 –0.19%

Silicones Low 7-1062 3-6 35 –0.15%Addition Extrude (Kerr Mfg Co, Romulus, Mich.) Medium 7-1140 2%-5% 30 –0.17%

High 7-1125 2%-3% 60 –0.15%High/Medium 7-1125/7-1140High/Low 7-1125/7-1062Very high 1%-2% 50-75 –0.14%

Condensation Elasticon (Kerr Mfg Co, Romulus, Mich.) Very low 7-1160 4%-9% 15-30 –0.60%Very high 7-1160 2%-5% 50-65 –0.38%

Polysulfide Permlastic (Kerr Mfg Co, Romulus, Mich.) Medium 7-1259 11%-15% 30 –0.45%High 9%-12% 35 –0.44%

*Italicized areas highlight impression materials that were tested for rotational torque displacement only. Bold areas highlight impression materials that were testedfor rotational torque displacement and for solid cast accuracy.

as the interaction effect between torque value andimpression material. Thereafter, the 5 torque values foreach impression material group (N = 2) were averagedand statistically compared among impression groupswith a 1-way ANOVA (α=.05). A post hoc Ryan-Einot-Gabriel-Welsch multiple range test (REGWQ) was usedto compare the mean torque values of the impressionmaterial groups.

Impression material accuracy

Thirty impressions were made of the master model,10 each of the 3 impression materials that haddetectable torque values: medium polyether; high addi-tion silicones; and medium polysulfide (Table I, bold-highlighted materials). Polyether was dispensed in anelectric mixing and dispensing machine (Pentamix,ESPE-Premier, Norristown, Pa.); addition silicone wasmixed and dispensed through an automixing system;and polysulfide was hand mixed and dispensed with aplastic syringe (Elastomer Syringe, ESPE-Premier).

Stainless steel abutment replicas (DCA 174, NobelBiocare USA Inc) were hand-tightened carefully with15 mm guide pins to the 5 direct impression copings ineach impression. Impressions were poured 30 minutesafter removal from the master model to simulate a clin-ical situation. As recommended in a previous study,14

impressions were poured in Resin Rock material (WhipMix Corp, Louisville, Ky.) that was vacuum mixed withdistilled water, in accordance with the manufacturer’sinstructions. Experimental implant casts were allowedto set for 1 hour before the guide pins were unscrewedand the impression was removed. One experimentalcast was poured from each impression producing 10casts per group. Any debris remaining on the abutmentreplicas was removed. All experimental implant castswere numbered and stored in ambient conditions for atleast 24 hours.36

Five 1.98-mm steel balls (McMaster-Carr, Aurora,Oh.) were placed on the central screw access channel ofthe abutments to provide a reliable central reflectivereference (Figs. 4 and 5). Linear distances between thesteel balls were measured with a traveling microscope(model MM-11, Nikon Corp, Tokyo, Japan), whichwas connected to an internal light source (UniversalEpi-Illuminator, Nikon Corp) and was capable ofrecording the x-, y-, and z-axes to an accuracy of±0.5 µm. The microscope was connected to a digitalreadout counter (SC-111, Nikon Corp). Alignment ofthe cross hairs with respect to the movable counter pro-vided the x and y coordinates, while the focus of themicroscope lens provided the z coordinate (Fig. 5).

The middle abutment replica, C, was used as a ref-erence on each cast for the distortion measurements ofthe remaining steel balls/abutment replicas. Thus,measurements were made of CA, CB, CD, and CE forall experimental casts. The counter was moved mechan-ically to align the steel ball on the abutment replica Cunder the microscope lens (Fig. 4), thereby directingthe internal light source onto the steel ball and backthrough the lens (magnification ×25). As magnificationwas gradually increased to ×200, the focus on the steelball was standardized through the internal glass filter,which appeared as pits within the steel ball. The inter-nal light source aperture was reduced, and the crosshairs were aligned on the center of this reduced lightsource field of view. At this position, the digital readoutcounter was set to 0 for x, y, and z coordinates.

The described procedure was repeated for each ofthe remaining abutment replicas to be measured foreach cast. However, rather than zeroing the counterafter alignment of the cross hairs, measurements of thex, y, and z coordinates were recorded on a personalcomputer for CA, CB, CD, and CE. Each measure-ment was taken on 3 separate occasions and then aver-aged. A 45-minute time limit was observed for eachmeasurement session to prevent eye fatigue.37

Using the Pythagorean theorem for a 3-dimension-al model [(x2 + y2 + z2)1⁄2], the linear distances betweenthe steel balls and the reference ball C were calculated(Fig. 6). The corresponding linear distance of the mas-ter model, namely, CA, CB, and so forth, was then sub-tracted from each mean linear distance of the experi-mental cast, with the absolute value taken of the result.The formula (CAexperimental – CAmaster = [A]) providesan illustration for the derivation of an experimentalcast’s CA measurement to a measurement of [A], orthe absolute micron deviation of the experimental castabutment from the master model. The absolute microndeviation for each cast’s 4 linear measurements, that is[A], [B], [D], [E], were then averaged for each cast,resulting in a cast’s mean absolute cast error. Absolutemicron deviations of all casts’ linear measurementswere compared statistically using a repeated measures



Fig. 4. Microscope lens of measurescope directly over steelball on abutment replica.

ANOVA (α=.05) to evaluate within-group, between-group differences, and the variables’ interaction effect.As illustrated, positive and negative linear distanceswere used to calculate [A]; however, only absolute(positive) values were compared for statistical analysis.A 1-way ANOVA (α=.05) was then used to evaluatethe significance among the material groups’ meanabsolute cast errors. Finally, a post hoc using REGWQwas used to rank the material groups’ mean absolutecast errors.

A measurement error (SD) of 3 µm was computedby measuring the distance between abutment replicas Aand E on the master cast 10 times. The SAS statisticalprogram35 was used to compute the statistical analyses.

RESULTS

Of the impression materials tested (Table I), torquevalues were detected for only 3: polyether (medium),addition silicones (high), and polysulfides (medium)(Fig. 7). Impression coping position did not produce astatistically significant difference within material

groups’ torque values (P=.1866), and a significantinteraction effect was not identified between impres-sion coping position and impression material(P=.4574). Notably, mean torque values differed sig-nificantly among impression material groups (P=.001),with the highest overall torque values identified forpolyether (medium), followed by addition silicone(high), and then polysulfide (medium) (Table II).

Similarly, regarding measures of accuracy within-group absolute micron deviations ([A], [B], [D], [E])did not reveal significant variation (P=.6881), and no


MARCH 2000 327

Fig. 5. Diagram of traveling microscope setup with implant cast and steel ball on abutmentreplica.

Table II. Ryan-Einot-Gabriel-Welsch multiple range test(REGWQ) groupings (P>.05) for torque measures

Mean SD REGWQMaterial N (×10–3 mN) (×10–3 mN) groupings

Polyether 2 141.3 0.4 AAddition silicone 2 71 6.4 BPolysulfide 2 51.5 7 C

significant interaction effect was found (P=.7167).One-way ANOVA (P=.0086) revealed a significant dif-ference among material groups’ mean cast errors. Onthe basis of further analysis, implant casts made frompolyether (medium) or addition silicone (high) impres-sions presented significantly less cast error than castsmade from polysulfide impressions (Table III).

DISCUSSION

Methodologic and clinical considerations shed lighton the relevance of these findings. The sensitivity of theCompudriver device (Consolidated Device Inc, City of

Industry, Calif.) was used arbitrarily as a selection crite-rion for differentiating between impression materialgroups to be tested in the accuracy phase of this study.Thereby, impression materials that lacked rigidity toprevent possible rotation of the copings were eliminat-ed from further consideration for viable accuracy. Sev-eral impression materials were also removed from con-sideration completely, as they were too difficult todeliver with a plastic syringe, making them less clinical-ly attractive, namely, polyether (high), polysulfide(high), and addition silicones (very high). Althoughadditional information may have been gatheredthrough use of more sensitive torque detection instru-ment, the significance of such information is limited.

A relative comparison of materials’ rigidity providesthe immediate, clinically applicable data, given that nodefinitive standard exists regarding the amount of resis-tance required to prevent accidental rotation of a



Fig. 6. Calculation of linear distance between 2 steel balls.

Fig. 7. Comparison of tested direct implant impressions fortorque and group mean absolute cast error.

Table III. Ryan-Einot-Gabriel-Welsch multiple range test(REGWQ) groupings (P>.05) for mean absolute cast error

Tukey’sMaterial N Mean (µm) SD (µm) groupings

Polyether 10 16.2 8.8 AAddition silicone 10 15.2 8.2 APolysulfide 10 26.2 6.7 B

square Nobel Biocare impression coping in an implantimpression. Results of our arbitrary selection criteriacoincide with impression materials that will most likelybe used for direct square implant impressions. Forinstance, polyether is recommended repeatedly in thedental literature.12,18-22,25,28-31 Addition silicones arerecommended as well,15,16,32 and are the preferredfixed prosthodontic impression material as taught inUS dental schools (70% or 42/53 schools).38 Polysul-fide, although not mentioned in the implant literature,is the preferred removable prosthodontic impressionmaterial as taught in US dental schools (48% or 47/54schools).39

From a clinical standpoint, results of this study sup-port the use of polyether for completely edentulousmulti-implant impressions. The rigidity of polyetherprovides resistance to the accidental displacement ofthe impression coping in the implant impression. How-ever, use of polyether for an impression of a partiallyedentulous arch also presents increased difficulty forintraoral removal of the impression. High consistencyaddition silicones and medium consistency polysulfidesare viable alternative materials of choice for experiencedpractitioners. Addition silicone with its more favorablemodulus of elasticity (rigidity)40 allows easy removal ofthe set impression.

Other suggested material combinations that werenot tested in this study include the use of very highconsistency or putty and low consistency wash, as test-ed by Barrett et al,15 and the use of adhesive surround-ing the impression copings. This concept of using ahigh and low consistency impression material is bor-rowed from techniques used in fixed prosthodontics.The low consistency impression material is syringedinto the sulcus of the prepared tooth, whereas highconsistency material helps force the low consistencymaterial into the sulcus.41 The lack of detectabletorque when using high/medium or high/low consis-tency impression material shows no advantage in usingit for direct implant impression. The design of theimplant impression coping may also be a relevant factorto consider. However, the design of most implantimpression copings is not intricate enough to requirethat a low consistency impression material be syringedaround them.

Addition silicones and polyether for direct multi-implant impressions for edentulous arches producesimilarly accurate solid implant casts, results consistentwith those recorded previously for an indirect implantimpression technique by Barrett et al.15 The externalvalidity of this conclusion, although limited to these 2studies, is noteworthy, given the significantly differentmethods of distortion measurement and analysisbetween the 2 studies.

To elaborate, distortion can be defined and mea-sured as “absolute” or “relative,” depending on the

point of reference from which the distortion is mea-sured.42 Barrett et al15 used absolute distortion analy-sis, whereby the point of reference is an external refer-ence point, namely, not include the impression copings.In contrast, this study, and many other distortion stud-ies, used relative distortion analysis, whereby one of theabutment replicas/impression copings is used as thereference to which the distortion of the other replicas/impression copings are measured.16,17,21,43 It may beargued that the use of relative distortion analysisprovides more clinically relevant data than absolute dis-tortion analysis. The implant prosthesis connects allabutments together. Therefore, the amount of strain inthe implant prosthetic–implant bone system is relatedto the relative position of the implant abutments to oneanother and not to an external reference point.

Another methodologic difference requires com-ment. The study by Barrett et al15 evaluated the accu-racy of the implant impression itself, as did Phillips etal.21 Using this method requires that follow-up studiesbe completed to determine the resultant accuracy ofthe implant cast, with the appropriate die material, toprovide data from a clinically relevant end product,such as the solid implant cast. Evaluating the accuracyof the implant impression with reference to a resultingsolid implant cast, as completed in this study, eliminatesthe need for follow-up studies and has become a stan-dard method across the majority of implant impressionaccuracy studies.12,16-20,25,43

This study also evaluated the accuracy of the relativeposition between the implant abutments through the useof steel balls on the abutment replicas, similar to Carr andMaster’s method.43 The purpose of this study was not toevaluate the implant abutment-to-framework relation-ship; this study only evaluated the resultant translationaldistortion (x-, y-, and z-axes) of the abutment replicas toone another, and not more complex rotational distortionthat occurs in implant prosthodontics.2-6,21,22,45-47 Thesignificant difference detected among impression materi-al groups indicates that the method of this study wasappropriately sensitive.

To validate this study, a long-term prospective clinicalstudy would have to be performed with preliminary dataavailable from this study. Patients requiring a particulartype of implant retained prosthesis would be dividedinto 2 groups. The patient’s definitive implant prosthe-sis would be fabricated to fit their master cast accuratelyusing either “laser welding of titanium”7,8 or “electricdischarge machining”9-11 method. For 1 group, themaster cast would be made from a direct implant impres-sion from addition silicone (high) or polyether (medi-um), and for the other group, the impression would bemade from polysulfide (medium). The fit of the pros-thesis would not be adjusted intraorally for every stageof the prosthesis fabrication procedure. The 2 groupswould then be evaluated longitudinally.


MARCH 2000 329

CONCLUSIONThe properties of an impression material, including

rigidity and accuracy, can influence the accuracy of theimplant impression, the accuracy of the solid implantcast, and ultimately, the accuracy of the cast implantframework. Choosing an impression material for multi-implant–retained prosthesis requires consideration of sev-eral factors, including material accuracy, clinician’s expe-rience with material, length of time before the impressionis poured, and amount of intraoral undercuts.

Within the limitations of this study, torque requiredto rotate an impression coping in the impression wassignificantly different (in descending order) from eachother: polyether (medium), addition silicone (high),and polysulfide (medium). Implant cast made frompolyether (medium) or addition silicone (high) was sig-nificantly different from cast made from polysulfide(medium). New practitioners to the specialty ofprosthodontics may prefer using polyether (medium),given its greater overall rigidity. The type of materialused for either the completely or partially edentulousmulti-implant impression will depend on which factorsare important to the practitioner.

I would like to thank Drs Steve Rosenstiel and Alan Carr for theirencouragement and review of the manuscript. Thanks also go to DrWilliam Johnston for the statistical assistance and Dr PeterMonaghan for his suggestions regarding the measuring technique.

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SECTION OF RESTORATIVE DENTISTRY, PROSTHODONTICS AND

ENDODONTICS

COLLEGE OF DENTISTRY

THE OHIO STATE UNIVERSITY

305 W 12TH AVE

COLUMBUS, OH 43210-1241FAX: 614-292-9422E-MAIL: [email protected]

Copyright © 2000 by The Editorial Council of The Journal of ProstheticDentistry.

0022-3913/2000/$12.00 + 0. 10/1/104915doi:10.1067/mpr.2000.104915


MARCH 2000 331

A retrospective study of 50 treatments using an applianceto produce localized occlusal space by relative axial toothmovementGough MB, Setchell DJ. Br Dent J 1999;187:134-9.

Purpose. This article describes the results of the treatment of 50 persons with a “Dahl”-typeappliance at the Eastman Dental Hospital, London, U.K., from 1981 to 1994. Studies by Dahlhave shown that the placement of a “partial bite raising appliance” on the maxillary anterior teethmay be used to create localized occlusal space before restoration of teeth. The space being pro-duced by the teeth in contact with the appliance being intruded and those out of contact extrud-ing. The aim of this retrospective clinical audit was to assess the outcome of using similar appli-ances placed in all regions of the mouth and the factors that may influence the outcome of treat-ment.Material and methods. Fifty appliances were used in 45 patients whose age ranged from 20 to70 years (median 37 years of age); 54% of patients were women. Appliances were used in the fol-lowing situations: attrition (19%-38%); erosion (11%-22%); total tooth wear (30%-60%); extrusion(17%-34%); iatrogenic (2%-4%); and lack of space after adult orthodontic treatment (1%-2%). Sev-enty-eight percent were cemented to teeth and 22% were removable. In addition, 64% wereplaced in the anterior arch (32% in the posterior) and 76% were placed on the maxillary arch (24%on the mandibular arch). Duration of treatment ranged from 1 month to 24 months, with a meantreatment of 5.9 months. After treatment, teeth were restored with definitive restorations, includ-ing conventional crown, fixed partial dentures, resin-retained fixed partial dentures, or hybridfixed prostheses.Results. Success rate of treatment was high (96%), with only 1 appliance in place that producedno useful tooth movement. All appliances produced enough space for restorations to be placedconservatively when given enough time to act.Conclusion. This type of treatment provided a conservative, predictable, and effective method togeneral localized occlusal space before prosthetic restoration. 11 References. —RP Renner

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