A Professional Courtesy of: James E. Metz, D.D.S.General Dentist

Diplomate, American Board of Dental Sleep Medicine

1271 E. Broad StreetColumbus, Ohio 43205

(614) 252-4444 • Fax: (614) 252-6474www.ColumbusDentistry.com

Memberships:American Dental Association • Ohio Dental Association • Columbus Dental Society

American Academy of Restorative Dentistry • International Academy of Gnathology • American College of DentistsEuropean Academy of Dental Sleep Medicine • American Academy of Dental Sleep Medicine • American Academy of Sleep Medicine

The design of a Kennedy Class I removmodified with implants placed in the mimplants wi'5 MfifSjfi support the distal ««

lartial denture can be;gions ;ese

• ies or7TH-SI : rEDR.

As new materials and techniques have been introduced to the profession,removable prosthodontics has evolved over the past 30 years. Althoughmany of the basic principles have not changed, these new developmentshave enhanced patient satisfaction with removable dental prosthesesand have had a major impact on improving the clinical outcomes oftreatment. This issue of Prosthodontics Newsletter reviews a series ofclinical and in vitro studies that investigated advances in removableprosthodontic materials and techniques.

AKennedy Class I removable par-tial denture (RPD) possessesbilateral extension bases. This

type of RPD can pose more problemsfor patients compared with RPDs forother classifications of partial eden-tulism. An all-tooth-supported RPD(Kennedy Class III) often offers a betterprognosis than that of a Class I RPD.

It has been postulated that patientsatisfaction with a Class I partiallyedentulous situation can be im-proved with the incorporation ofdental implants in the RPD design.The 2 approaches to incorporatingimplants into an RPD design havebeen described as implant-supported

(continued on next page)

Maxillaryirhplcint-supporiedOverdentures

>- Color SiabiiHy ofAcrylic Resin Hffifidal Teeth

I . Wear ofResin Artificial Teeth

ProsthodonticsNewsletter™

Implant-tooth-supported RPDs(continued from front page)

and implant-assisted designs. Animplant-supported RPD designincorporates healing caps to pro-vide support for the extensionbase. An implant-assisted RPDuses resilient implant attachmentsto provide additional retention.

A systematic review of articles de-voted to the clinical outcomes of im-plant-supported/implant-assistedRPDs was conducted by Shahmiriand Atieh from the University ofOtago, New Zealand. Nine articleswere selected for the review. Thedata included 183 implants in 94 pa-tients. Follow-up time ranged from3 weeks to 120 months. All RPDs hadbilateral extension bases with im-plants placed bilaterally in the molarregions (see cover illustration).

Results indicated favorable out-comes associated with implant-sup-ported/implant-assisted RPDs com-pared with conventional Class IRPDs. Advantages included

X enhanced stability and retention

>• improved esthetics

>• improved oral hygiene

; reduced bone resorption be-neath the denture bases

>- ease of converting to a conven-tional RPD if there were implantfailures

>• ability to modify unfavorablearch configurations

>- improved patient satisfaction

>• less prosthetic maintenance

X ability to reduce the extension ofthe RPD bases

>• lower cost compared with a fixedimplant-supported prosthesis

>• reduced potential for the combi-nation syndrome

Comment

While none of the studies in thisreview was a randomized, con-trolled clinical trial, results appearvery promising. The prostheses inthis review were not without main-tenance problems; however, pa-tient satisfaction with this relativelyuncomplicated and cost-effectivetreatment method was improved.Further studies are necessary to de-termine the long-term results of thistreatment approach.

Shahmiri RA, Atieh MA. Mandibular Ken-nedy Class I implant-tooth-borne remov-able partial denture: a systematic review.] Oral Rehabil 2010;37:225-234.

Maxillary

Overdentures

M illed bars attached tomaxillary dental implantscan provide rigid support

and stability for an implant-sup-ported overdenture. Krennmairand Piehslinger from the Univer-sity of Vienna, Austria, conducteda retrospective study of the clini-cal outcomes of 2 different milled-bar designs.

Thirty-one patients were includedin the study; 15 had 4 implants inthe anterior portion of the maxil-lae, placed anterior to the maxil-lary sinuses. These patients weretreated with a 1-piece bar thatextended across the dental archand incorporated bilateral can-

tilevers. Sixteen patients weretreated with 2 free-standing barson either side of the dental arch.These 2 unconnected bars weresupported by 6-8 dental implants.

All overdentures were U-shaped,had been in function for at least3 years (mean, 4.6 ± 1.3 years; agerange, 3-8 years), were designedwith a 2-4° taper to the bars andwere provided with additionalretentive devices (Preci-Vertex;Alphadent Co., Ltd., Seoul, SouthKorea). Overdentures in bothgroups were metal reinforced, andall incorporated 12 artificial acrylicresin teeth.

Variables included the amount ofsupporting area generated by thebars and postinsertion mainte-nance. The bar-generated support-ing area was calculated mathemati-cally after drawing lines connectingthe most anterior portion and themost posterior portion of the bar toproduce a cross-arch, 4-sided poly-gon (Figure 1).

Maintenance complications wereevaluated as either implant-compo-nent complications or prosthetic-component complications. Implant-component complications includedimplant loss or fracture, abutmentscrew loosening and abutment orbar fracture. Prosthetic-componentcomplications included retentivematrix activation or replacement,fracture or replacement of artificialteeth, fracture of the denture, den-ture border adjustment, overdenturerebase and maintenance of opposingprosthesis.

Results indicated that the meansupporting area for the 1-piece,cross-arch bar was 962 + 84 mm2

and for the double-bar design,

Summer 2010

1015 ±118 mm2, a difference thatwas not significant. The 1-piece-bargroup experienced 17 prostheticmaintenance problems (0.20 prob-lems/year/patient) ; the double-bargroup experienced 19 prostheticproblems (0.22 problems/year/pa-tient). Screw loosening was theonly implant-component complica-tion evident in both groups. Allother complications involved pros-thetic components. These resultswere not significant.

Comment

With no significant differences inclinical outcomes between the2 designs, it is difficult to claimeither approach as superior. Pla-cing 4 implants in the maxillarybone anterior to the maxillarysinuses is a much less complicatedsurgical procedure. When implantsare placed in the posterior maxil-lae, bone augmentation of thesinuses is commonly required, aprocedure that will complicate thesurgical phase of the treatmentsubstantially and prolong the du-ration of the treatment time. A lesscomplicated surgical phase wouldhave advantages that would not

affect the clinical outcome of thefinal prosthetic treatment.

Krennmair C, Piehslinger E. Removableimplant-supported maxillary prosthesesanchored on milled bars: a retrospectiveevaluation of two concepts. Int f Pros-thodont 2009;22:576-578.

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Commonly used in removableprosthodontics, acrylic resinartificial teeth can become

discolored over time. Intrinsic stain-ing can occur with aging or degra-dation of the material resulting fromalterations in physical and chemicalconditions, such as thermal changesand humidity. Extrinsic factors pro-duce discoloration from absorptionand adsorption.

Assungao et al from AragatubaDental School, Sao Paulo State Uni-versity, Brazil, investigated thecolor stability of 10 commerciallyavailable acrylic resin artificialteeth. The brands they studiedincluded the following:

>• Art Plus (Dentsply Ind. e Com.Ltd., Petropolis, Brazil)

X Biolux (Vipi Ind. Com. Ltd.,Pirassununga, Brazil)

> Biotone IPN (Dentsply Ind. eCom. Ltd.)

>• Magister (Heraeus KulzerGmbH, Hanau, Germany)

>- Mondial 6 (Heraeus Kulzer)

>• Premium 6 (Heraeus Kulzer)

> SR Vivadent PE (Ivoclar Viva-dent, Inc., Amherst, N.Y.)

>- Trilux (Ruthibras Imp. Exp.Com. de Materials Odontol. Ltd.,Pirassununga, Brazil)

>• Trubyte Biotone (Dentsply Ind. eCom. Ltd.)

>• Vipi Dent Plus (Vipi Ind. Com.Ltd.)

Each group (n = 24) was dividedinto 2 subgroups. One subgroupwas subjected to a simulated den-ture-base processing cycle in a mi-crowave oven (500 W for 3 min-utes) ; the other subgroup wassubjected to a simulated conven-tional water-bath polymerizationcycle (74°C for 9 hours).

All specimens were then thermalcycled (5-55°C, 30-second dwelltime, 5000 cycles). Specimen colorswere measured with a spectropho-tometer with the use of the CIEL*a*b* system. Measurements weremade at baseline (B), after simula-tion of polymerization (P) and afterthermal cycling (T). Color changes(AE) between PB, TP and TB wereevaluated. Results indicated thatminor AE changes occurred afterpolymerization and after thermalcycling. There were no significantdifferences between the 2 polymer-ization techniques. The greatestchanges were evident in Biotone IPNand SR Vivodent PE teeth. Neverthe-less, in all groups and under all con-ditions, the AE change was <3.3.Changes <3.3 are considered clini-cally acceptable.

Comment

Color changes resulting from poly-merization of the denture base ornormal aging, including tempera-ture changes in the mouth duringnormal function, are not likely toresult in any clinically detectable

ProsthodonticsNewsletter™

alteration in the shades of theteeth studied. The authors selectedonly 1 shade for each brand oftooth. Because each manufacturerhas its own shade selection guide,shades for this study could not bestandardized. Those selected forthe study tended to represent themost popular shades; however,it should not be assumed that sim-ilar results would occur with dif-ferent shades of the same brandof tooth.

Assuncao WG, Barao VAR, Pita MS,Goiato MC. Effect of polymerizationmethods and thermal cycling on colorstability of acrylic resin denture teeth.] Prosthet Dent 2009/702:385-392.

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R esin artificial teeth, com-monly used with removabledental prostheses, are sub-

ject to wear over time. Occlusalwear is undesirable and can resultin loss of occlusal stability. Manu-facturers of artificial teeth claimthat wear resistance has been im-proved by new developments inthe chemistry of the resin materi-als used to manufacture the teeth.

A study by Stober et al from Heidel-berg University Hospital, Germany,evaluated the 3-body wear resis-tance of 11 commercially availableartificial teeth. Three types of artifi-cial teeth were studied:

>• Conventional and cross-linked acrylic resin teeth:SR Orthotyp PE (Ivoclar Viva-dent AG, Schaan, Liechten-stein), Orthognath (HeraeusKulzer GmbH, Hanau, Germany),

Premium 8 (Heraeus KulzerGmbH), SR Postaris DCL (Ivo-clar Vivadent AG), TrubytePortrait (Dentsply International,York, Pa.) and Artiplus (Degu-Dent GmbH, Hanau, Germany)

>• Composite resin teeth withinorganic fillers: SR OrthotypPE (Ivoclar Vivadent AG) andVitapan (VITA Zahnfabrik, BadSdckingen, Germany)

>• Composite resin teeth withinorganic nanofillers: NCVeracia Posterior (Shofu DentalGmbH, Ratingen, Germany),e-Ha (Heraeus Kulzer GmbH)and Mondial (Heraeus KulzerGmbH)

Human enamel and feldspathicceramic artificial teeth served ascontrol groups.

Tests were performed in a wearmachine, with a foxtail millet sus-pension as the abrasive material.After 100,000 wear cycles, the lossof material as a result of wear wasmeasured with a profilometer. Re-sults indicated that none of the ar-tificial teeth had 3-body wear re-sistance comparable to that ofhuman enamel or ceramic artificialteeth. Composite resin teeth withconventional fillers were more re-sistant to wear than were conven-tional or cross-linked acrylic resinteeth without fillers. The incorpora-tion of nanofillers did not result inimproved wear resistance.

Comment

With implant-supported removableprostheses, patients can generateconsiderably more force than can begenerated with conventional re-movable prostheses. As a result, ac-celerated wear of the artificial teeth

has been observed. The results sug-gest that composite resin teeth withconventional inorganic fillers willdemonstrate improved resistance towear compared with acrylic resinteeth without fillers and nanofilledcomposite resin teeth. Nevertheless,ceramic artificial teeth provide thebest approach to reducing the po-tential for accelerated wear.

Stober T, Henninger M, Schmitter M, et al.Three-body wear of resin denture teeth withand without nanofillers. ] Prosthet Dent2010;103:108-117.

In the Next issue

Retention of pressedceramic crowns

- Fracture rate of pressedceramic crowns

Effect of cuspal inclination onstress distribution withinpiunt-i-.i ippooed crowns

Our next report features adiscussion of fhese issues andthe studies that analyze them,as well as other articlesexploring topics of vital interestto you as a practitioner.

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