A method to compare costeffectiveness of dental treatments: adhesive bridges compared to conventional bridges
Nico H. J. Creugers and Arnd F. Kayser Department ot Oral Function and Prosthetic Dentistry. TRIKON: Institute for Dental Clinical Research, University ot Niimegen, Nijmegen the Netherlands
Creugers NH,I, Kayser AF: A tnclhod lo cotnpitre cosl-clTectivctiess ordeiititl tfcattiictTts; adhesive bridges eotnpared to cotivetilional bridges, Cotntinmity I5cnt Otal Fpidctmiol 1992; 20: 280-3, Abstract - The cost-elTcctivctiess of a dctiUtI resloralion depetids pritnarily on the durability and the cost ofthe restoration. In this teporl a method is described to cotTtpare the cost-effectiveness using the durability data of adhesive bridges and conventional bridges. The study shows that, for the situation in the Netherlands, (he bteakeven point for equal cost-effectiveness cotnpared lo conventional bridges is achieved when the SO'^Ii survival for adhesive bridges is approxitnately 6,5 yr. Clinical data indicate a higher cost-effectivettess for anterior adhesive bridges. The method described in this report is consideted to be useful lor cotnparing cost-effectiveness of dental restorations iti different situatiotis.
The advantages of adhesive bridges cotnpared to conventional bridges, as suggested by several investigators, are 1) limited toi)th preparation, 2) altnost reversible procedures, 3) no pulpal involvement, 4) tio requiretnents for anesthesia, 5) less titne-consumtng procedttres, and 6) lower cost (1 3). There are several criteria which should be included in the evaluatioti of dental treatments. Besides a nutnber of technical and biological criteria, the econotnic aspect is a sigtiiftcatit factor in the sticcess of a dental treatment innovation. However, tnore itnportant Ihan the cost factor is the cost-elTectiveness. To be an eeonotnic success form the patients' (or from a health care insurance institution's) point of view, there is a need lor an equal or even higher cost-effectiveness of adhesive bridges compared to conventiotial bridges. 7 he cost-ef/ectiyeness of a dental restoration procedure is ditectly related to both the benefit (effectivity) ol'the restoration and the efficiency (reversely proportional to the cost) of the restoration procedure. The beneftt of a dental treatment may be considered its service, which is a cotnbination of futiction, convenience and tltirability, Assutning that esthetics, futiction and cotnfort of two different trealtneiUs are tnore or less similat\
the diffetence of cost-effectiveness of both treattnents is tnainly caused by differences in cost and durability. The cost of prosthetic detital treattnents depends on; 1) the dentist fee, and 2) the expenses for the dental laboratory. In many western countries both the denlist fees and the laboralory fees are regulated in one way or another. Where the fees are regulated, the efficiency (which is the inverse ofthe cost) may be calculated in an easy way. Where the fees ate nol determined by any professional organizatioti or govei nment policy, the efficiency is difficult lo compute. Dentist fees based on tteattnent times show a gteat variation since the Ireatmenl titnes of detilal restoratiotis vary substantially (3 6), The cost-effectiveness of a specific dental tteattnent can be cotnpttled on the basis of benefit and cost by comparitig it to a reference (7): Cost-effectiveness (real) = Cost-effectiveness (reference) X Effectivity x Efficieticy = Cost-effectiveness (reference) benefit (real) x cost (refcreticc) X
benefit (reference) x cost (real) A btcakcveti point of the cosl-cficctiveness of treatmetit A cotnpated to treatmenl B is achieved whete:
Key words: cost-effectiveness; dental restoration Nico H. J. Creugers. Llniversity of Nijmegen, Dental School. Dept. ot Oral Function and Prosthetic Dentistry. Philips van Leydenlaan 2S 6525 EX Nijmegen, the Netherlands Accepted for publication 15 October 1991
Cost-effectiveness,, Cosl-cffecliveness,,
I
When the effectivity of both the treatments is proportional lo the durability the Ibitntila for cost-cO'ecliveness is: Cost-effectiveness, A, = Cost-effeclivetiess,|,| durability,;\i x cost,ii, durability,1,1 xcost,^) This agaiti tneatis that equal cosl-elTecliveness is achieved wlieti (.iurabilily (A) =
durability||,,xcost,, cost,.
With tespect to this fortnula the durability (lifetitne expectation) needed to achieve equal cost-effectiveness tnay be calculated for any particular dental resloratioti in a specific sitttation, by cotnparing it to the altertiatives for that situation. However, in oral health cate one has to cotnpare means of durability values (lifetitne expectations) iti otder lo give an estitnation of the cost-effeclivcness. The aim of lliis report is lo present a method for assessment of the cost-effectiveness of adhesive bridges cotnpared to convetitiotial bridges on the basis of cost and dttrabilily data from llie lileralure.
Cost-effectiyeness of dental restorations
Materials and methods I n comparing adhesive bridges to conventiotial bridges thete are sotne utiknown and variable factors; tlie factor cost is variable atid ofien differs substantially frotn one cotmtry to atiother, while t h e factor benefit (i.e. dttrability) has to b e based on incotisislcnl lesearch dala. In the Netherlands, where both ihc dentist fees and dental laboratory fees a r e regulated and prescribed by law (COTG*, VLHT1), the ratio ofthe costs o f a 3-utiit adhesive bridge (potcelain fused-to-rnelal, uoti-precioiis tnelal) and a compatable conventional bridge (potcelain fused-to-tnetal. High silver palladiu m alloy) is 1 to 3 approxitnately. This m e a n s that ihe efficieticy of an adhesive bridge in the Netherlands is apptoximately three titnes better thati that of a convetitiotial bridge. Foi' the assesstnenl of llie survival of adhesive bridges, the d a t a ofllie Nijmegen adhesive bridge trial were used because ihey provide confidence intervals and sufficietit details for interpretation (8, 9), The tesulls of this study show a survival rate of 15% after 7.5 yr for atiterior bridges (10). Other longitudinal studies revealed survivals in t h e same range, and an atialysis of clitiical sludies concerning the survival rales in different studies resulted iti ati overall survival (for both anlerior and poslerior adhesive bridges) of 74% afler 4 yr (1 I), For cotivetitional bridges, longiuiditial clinical sttidies show iti getieral a survi\al r a t e of 80-90y(i after 10 yr atid approximately 50% after 20 yr (12-15). The failu r e rale per year tends to increase with time. Several authors have postulated t h a t the 5O'yii survival rate of eonvetitiotial bridges is in the range of 20 25 yr (13, 16), Fig. 1 presents a cost-bcncfil plot. This is a schetnatic graphical represetitatioti of the relatiotiship betweeti dttrabilily a n d cost for a constant value of the costeffectiveness. Line "a" represents the ratio of cost and durability for a ccrlaiti constant cosl-effectivcticss of the relerence. Field H represents a higher costeffectiveness cotnpared lo the relerence a n d field L represents a lower cost-effectiveness. The iiiclitie (a) of litie a is directly related to the dtitability atid cost • Centraal Orgaan Tarieven Cic/ondheids/org. UPT-trievenlij.st, 1991. f Vereniging Laboratoriumhoudende landtechnici. Tarievenlijst, 1991.
ol' the reference. A decrease of the durability of the reference results in an increase of the area for higher cost-effeclivetiess, Assessmetil of cosl-effeclivetiess of adhesive bridges compared to conventiotial bridges is perfortned by a projection of the durability data of bolh resloraliotis in the cost-benefit plot. For cotnparison, tlic durability data were cotiverted to assessed 5O'/ii survival rates. The dttrability data of the investigated restorations were projected iti such a way thai they were related to the respective cost-levels. The assesstnent was caried
out for the cost-ratios 1 : 3 and 2: 3,
Results and discussion Wilh the data mentioned, il is possible to estimate the cost-effectiveness ol adhesive bridges by calcttlatitig the cost tor a particular situation while the assessmetit of the 5O'y!i survival is made on the basis of an estitnation. The assessed 50"/» survivals used in the calculations were 12 yr for atilerior adhesive bridges atid 20 yr for cotivcntiotial bridges. Iti Fig. 2 the costs of adhesive bridges cotnpared to convetUional bridges are choseti lo be iti a ratio of 1 to 3. This ratio is representative for the situation in the Netherlands. It shows that anterior adhesive bridges are projected in the field of a higher cost-effeetivetiess. Iti this way the efficiency (i.e. the respective eosts) inlluetices the iticlities ofthe lities A atid C atid the lines beeotne tepresetitative for the cosl-effeclivetiess. The assesstnent of Ihe 50'% survival is based upon the resttlls of our owti clitiical study (i.e. poitit 3, w hieh is the projeciioti
281
ofthe 7.5 yr survival rate). Point 2 represents the 50% survival of eonventional bridges and is extrapolated from the data metitioned before. Iti this figure point 4 represents the lifelitne expeetation tieeded for adhesive bridges to achieve equal cost-elTectivetiess when cotnpared to durability data of conventional bridges. This tneatis that a 5O'/'ii survival after approxitnately 6,5 yr is needed for adhesive bridges lo achieve equal cost-effectivetiess as for the convetitiotial bridges in the studies of V.At.t)i:RtiAtic. atid other researchers (13 15). The projectioti ofthe results of the anterior resin-bonded bridges frotn our study in the figure results in a distinct location in the field of higher productivity. When the results of a tneta-atialysis regarding durability studies were projected in this figute jusl equal or slightly higher cost-effectiveness for adhesixe bridges was seen (11). It should be noted that, posterior conventional bridges seetn to survive longer than atiterior cotivenlional bridges (17), while there are indieations that adhesive bridges behave in the opposite tnanner (13).' Fig. 3 shows that the presented tnethod of detertninalion of cost-effeetiveness is also possible with other data and thus useful for other situatiotis atid countries, ln this figute the cost ratio is chosen to be 2 10 3. ll is clear that the slope ofthe lines for adhesixe bridges has decreased. As a resttlt the lities for both Ihe atilerior and posterior bridges are tiow loeated DURABILITY 20.
DURABILITY
1/3 «
COST
Eig. /. CTraphical representation oi' the relationship of dnrability and cost for a certain con.stani cost-cflectivcncss (cost-benefit plot).
«
COST
Fig. 2. Durabilitx data for adhesive bridges and conventional bridges projected in the schematic cost-bencHt plot lor a cost ratio of 1 to .V 1; assessed 50" n siirvixal of anterior adhesive bridges, 2: reported 50" o survival of conventional bridges, 3; stirvival of anterior adhesive bridges, 4: breakeveti point for equal cost-effcctivcncss. .A: anterior adhesive bridges, C: conventional bridges.
282
CREtJGF.RS AND K A Y S I Z R
eratute (II), Another complication with posterior adhesive bridges is that the 20. evaluated popttlations were relatively small while the observation periods were relatively short. This tneans that the calculation of the cost-effectiveness of posterior adhesive bridges shottld be tnade 10. with extretne care. The data of posterior adhesive bridges are therefore excluded frotn our calculations. However, as tnentioned above, there are indications that the durability of posterior adhesive bridges is less than the durability of anterior adhesive bridges (8). The informa« COST tion about the lifetitne expectations of F'ig. 3. Durability data for adhesive bridges and conventional bridges projected in the scheanterior adhesive bridges indicates better matic cost-bcnelu plot for a cost ratio of 2 to cost-effectivcness for the situation in the 3. 1; assessed 50'!^. survival of anterior adhesive Netherlands. Allliough there are sotne bridges, 2: reported 5O'^i survival of convenlitnitations due to some sitnplifications, tional bridges, 3: survival of anterior adhesive bridges, 4: breakeven point for equal cost-efthe principles of the method retnains fectiveness. A: anterior adhesive bridges, C; valid in our opinion. conventional bridges. It is important to note that the costeffectiveness calculation of adhesive in the fteld of lower cost-effectiveness. bridges, as presented in this study, is only However, the estimated confidence inter- a part ofthe trealment itnplications. The vals for anterior adhesive bridges (95'V!i different indicatiotis for the various reinterval; 68--80'^ survival after 7.5 yr constructiotis and the cotnplcxity of the (10)) may indicate the need for a correc- Iteatment also have an itnpacl on the tion when tnore long-term data beeotne cost and benefit of a treattnent. available. Another consideration in the cost-betiDespite Ihe fact that a nutnber of fae- efit analysis is the oral situation after tors in the cost benefit analysis are un- failure ofthe bridge, which is in favor of known or difficult to compare, it may be Ihe adhesive bridge. Due to biological concluded that the cost-effectiveness of effects, especially caries, the "rest-valtte" adhesive bridges is in general cotnparable of the abuttnent teeth may be substanto the cost-effectiveness of conventional tially decreased after failure of a convenbridges. In teality the cost-benefit plots tional bridge, tesulling in Ihe fabrication may be tnore complicated as the lifetimes of a new bridge, if this is possible at all. might not be directly ptoporlional wilh In ihis atialysis the survival of adhesive time. As a result of this, the value of the bridges was determined from the number cost-effectiveness (which is dependent on of detached bridges (8, I 1). Since adhethe durability data) can also show llueluations. Due to factors as tnaterial fatigue sive bridges are relatively easy to rebond the survival rates, as expressed in a per- atul loosening does not automatically centage per yeat\ tnay increase substan- lead to loss of the reconstruclion, the tially after 5, 10 or 20 yr (15), Moreover calculated survivals may be an undereslithe durability expectation is in reality not matioti ofthe number of bridges in funca single line but an area. Durability data tioti, tesulting in a too negative image. of adhesive bridges are still restricted to However, there are indications that the short- and mid-term studies. This means survival of tebonded bridges is not as that the assessment of the durability has good as the survival of originally bonded to be based on survival data, ineluding adhesive bridges (9, 18). confidence intervals. The Nijtnegen adWith respect to the durability of the hesive bridge trial was used for this pur- conventional bridges, the data reported pose because the reports of this study are divergent. The results of durability provided confidence intervals. With re- studies are expressed in a failure percenspect to the durability data of posterior tage per year, indicating indirectly the adhesive bridges it has to be tnenlioned survival pereentage, Howevet, many that there is substatitial variation in the sttidies do not give clear infortnation resurvival percentages presented in the lit- garding the quality of the surviving DURABILITY
populatioti, which may tesult iti a t o o positive image (12, 13) Esthetics and subjective comfort are also factors of benefit. These factors are difficult to quantify for populations of palieiits and therefore diffieult to include in calculations for cost-effeetivetiess However, in Ihis sludy the esthetic result and oral comfort of the evaluated restorations were eonsidered to be tnore o r less similar. There are other factors vvhiel-i were not iticluded, stich as the social costs for the patient (the titne needed to see the dentist) and psychological aspects (fear for dislodgetneiit, patients' satisfaction). More researeh needs to be dotie on these social and psychological ditnen, sions.
References t. CRliUGtiRS NH.I. Ctiniccd pcrftniiiaiiee of adhesive bridges. Thesis, I'tirosound liV Nijmegen, 19X7. 2. IVlAt(iNi:i.i.o Cl'. Adhi'isivprotlietik Klitij.. sclie und materiatkuiidticlie Aspekte. Berlin; Qtiintcssenz, 1991. 3. Vi:K/.i.ii)t:N CWG.IM, C't
Nico H. J. Creugers and Arnd F. Kayser Department ot Oral Function and Prosthetic Dentistry. TRIKON: Institute for Dental Clinical Research, University ot Niimegen, Nijmegen the Netherlands
Creugers NH,I, Kayser AF: A tnclhod lo cotnpitre cosl-clTectivctiess ordeiititl tfcattiictTts; adhesive bridges eotnpared to cotivetilional bridges, Cotntinmity I5cnt Otal Fpidctmiol 1992; 20: 280-3, Abstract - The cost-elTcctivctiess of a dctiUtI resloralion depetids pritnarily on the durability and the cost ofthe restoration. In this teporl a method is described to cotTtpare the cost-effectiveness using the durability data of adhesive bridges and conventional bridges. The study shows that, for the situation in the Netherlands, (he bteakeven point for equal cost-effectiveness cotnpared lo conventional bridges is achieved when the SO'^Ii survival for adhesive bridges is approxitnately 6,5 yr. Clinical data indicate a higher cost-effectivettess for anterior adhesive bridges. The method described in this report is consideted to be useful lor cotnparing cost-effectiveness of dental restorations iti different situatiotis.
The advantages of adhesive bridges cotnpared to conventional bridges, as suggested by several investigators, are 1) limited toi)th preparation, 2) altnost reversible procedures, 3) no pulpal involvement, 4) tio requiretnents for anesthesia, 5) less titne-consumtng procedttres, and 6) lower cost (1 3). There are several criteria which should be included in the evaluatioti of dental treatments. Besides a nutnber of technical and biological criteria, the econotnic aspect is a sigtiiftcatit factor in the sticcess of a dental treatment innovation. However, tnore itnportant Ihan the cost factor is the cost-elTectiveness. To be an eeonotnic success form the patients' (or from a health care insurance institution's) point of view, there is a need lor an equal or even higher cost-effectiveness of adhesive bridges compared to conventiotial bridges. 7 he cost-ef/ectiyeness of a dental restoration procedure is ditectly related to both the benefit (effectivity) ol'the restoration and the efficiency (reversely proportional to the cost) of the restoration procedure. The beneftt of a dental treatment may be considered its service, which is a cotnbination of futiction, convenience and tltirability, Assutning that esthetics, futiction and cotnfort of two different trealtneiUs are tnore or less similat\
the diffetence of cost-effectiveness of both treattnents is tnainly caused by differences in cost and durability. The cost of prosthetic detital treattnents depends on; 1) the dentist fee, and 2) the expenses for the dental laboratory. In many western countries both the denlist fees and the laboralory fees are regulated in one way or another. Where the fees are regulated, the efficiency (which is the inverse ofthe cost) may be calculated in an easy way. Where the fees ate nol determined by any professional organizatioti or govei nment policy, the efficiency is difficult lo compute. Dentist fees based on tteattnent times show a gteat variation since the Ireatmenl titnes of detilal restoratiotis vary substantially (3 6), The cost-effectiveness of a specific dental tteattnent can be cotnpttled on the basis of benefit and cost by comparitig it to a reference (7): Cost-effectiveness (real) = Cost-effectiveness (reference) X Effectivity x Efficieticy = Cost-effectiveness (reference) benefit (real) x cost (refcreticc) X
benefit (reference) x cost (real) A btcakcveti point of the cosl-cficctiveness of treatmetit A cotnpated to treatmenl B is achieved whete:
Key words: cost-effectiveness; dental restoration Nico H. J. Creugers. Llniversity of Nijmegen, Dental School. Dept. ot Oral Function and Prosthetic Dentistry. Philips van Leydenlaan 2S 6525 EX Nijmegen, the Netherlands Accepted for publication 15 October 1991
Cost-effectiveness,, Cosl-cffecliveness,,
I
When the effectivity of both the treatments is proportional lo the durability the Ibitntila for cost-cO'ecliveness is: Cost-effectiveness, A, = Cost-effeclivetiess,|,| durability,;\i x cost,ii, durability,1,1 xcost,^) This agaiti tneatis that equal cosl-elTecliveness is achieved wlieti (.iurabilily (A) =
durability||,,xcost,, cost,.
With tespect to this fortnula the durability (lifetitne expectation) needed to achieve equal cost-effectiveness tnay be calculated for any particular dental resloratioti in a specific sitttation, by cotnparing it to the altertiatives for that situation. However, in oral health cate one has to cotnpare means of durability values (lifetitne expectations) iti otder lo give an estitnation of the cost-effeclivcness. The aim of lliis report is lo present a method for assessment of the cost-effectiveness of adhesive bridges cotnpared to convetitiotial bridges on the basis of cost and dttrabilily data from llie lileralure.
Cost-effectiyeness of dental restorations
Materials and methods I n comparing adhesive bridges to conventiotial bridges thete are sotne utiknown and variable factors; tlie factor cost is variable atid ofien differs substantially frotn one cotmtry to atiother, while t h e factor benefit (i.e. dttrability) has to b e based on incotisislcnl lesearch dala. In the Netherlands, where both ihc dentist fees and dental laboratory fees a r e regulated and prescribed by law (COTG*, VLHT1), the ratio ofthe costs o f a 3-utiit adhesive bridge (potcelain fused-to-rnelal, uoti-precioiis tnelal) and a compatable conventional bridge (potcelain fused-to-tnetal. High silver palladiu m alloy) is 1 to 3 approxitnately. This m e a n s that ihe efficieticy of an adhesive bridge in the Netherlands is apptoximately three titnes better thati that of a convetitiotial bridge. Foi' the assesstnenl of llie survival of adhesive bridges, the d a t a ofllie Nijmegen adhesive bridge trial were used because ihey provide confidence intervals and sufficietit details for interpretation (8, 9), The tesulls of this study show a survival rate of 15% after 7.5 yr for atiterior bridges (10). Other longitudinal studies revealed survivals in t h e same range, and an atialysis of clitiical sludies concerning the survival rales in different studies resulted iti ati overall survival (for both anlerior and poslerior adhesive bridges) of 74% afler 4 yr (1 I), For cotivetitional bridges, longiuiditial clinical sttidies show iti getieral a survi\al r a t e of 80-90y(i after 10 yr atid approximately 50% after 20 yr (12-15). The failu r e rale per year tends to increase with time. Several authors have postulated t h a t the 5O'yii survival rate of eonvetitiotial bridges is in the range of 20 25 yr (13, 16), Fig. 1 presents a cost-bcncfil plot. This is a schetnatic graphical represetitatioti of the relatiotiship betweeti dttrabilily a n d cost for a constant value of the costeffectiveness. Line "a" represents the ratio of cost and durability for a ccrlaiti constant cosl-effectivcticss of the relerence. Field H represents a higher costeffectiveness cotnpared lo the relerence a n d field L represents a lower cost-effectiveness. The iiiclitie (a) of litie a is directly related to the dtitability atid cost • Centraal Orgaan Tarieven Cic/ondheids/org. UPT-trievenlij.st, 1991. f Vereniging Laboratoriumhoudende landtechnici. Tarievenlijst, 1991.
ol' the reference. A decrease of the durability of the reference results in an increase of the area for higher cost-effeclivetiess, Assessmetil of cosl-effeclivetiess of adhesive bridges compared to conventiotial bridges is perfortned by a projection of the durability data of bolh resloraliotis in the cost-benefit plot. For cotnparison, tlic durability data were cotiverted to assessed 5O'/ii survival rates. The dttrability data of the investigated restorations were projected iti such a way thai they were related to the respective cost-levels. The assesstnent was caried
out for the cost-ratios 1 : 3 and 2: 3,
Results and discussion Wilh the data mentioned, il is possible to estimate the cost-effectiveness ol adhesive bridges by calcttlatitig the cost tor a particular situation while the assessmetit of the 5O'y!i survival is made on the basis of an estitnation. The assessed 50"/» survivals used in the calculations were 12 yr for atilerior adhesive bridges atid 20 yr for cotivcntiotial bridges. Iti Fig. 2 the costs of adhesive bridges cotnpared to convetUional bridges are choseti lo be iti a ratio of 1 to 3. This ratio is representative for the situation in the Netherlands. It shows that anterior adhesive bridges are projected in the field of a higher cost-effeetivetiess. Iti this way the efficiency (i.e. the respective eosts) inlluetices the iticlities ofthe lities A atid C atid the lines beeotne tepresetitative for the cosl-effeclivetiess. The assesstnent of Ihe 50'% survival is based upon the resttlls of our owti clitiical study (i.e. poitit 3, w hieh is the projeciioti
281
ofthe 7.5 yr survival rate). Point 2 represents the 50% survival of eonventional bridges and is extrapolated from the data metitioned before. Iti this figure point 4 represents the lifelitne expeetation tieeded for adhesive bridges to achieve equal cost-elTectivetiess when cotnpared to durability data of conventional bridges. This tneatis that a 5O'/'ii survival after approxitnately 6,5 yr is needed for adhesive bridges lo achieve equal cost-effectivetiess as for the convetitiotial bridges in the studies of V.At.t)i:RtiAtic. atid other researchers (13 15). The projectioti ofthe results of the anterior resin-bonded bridges frotn our study in the figure results in a distinct location in the field of higher productivity. When the results of a tneta-atialysis regarding durability studies were projected in this figute jusl equal or slightly higher cost-effectiveness for adhesixe bridges was seen (11). It should be noted that, posterior conventional bridges seetn to survive longer than atiterior cotivenlional bridges (17), while there are indieations that adhesive bridges behave in the opposite tnanner (13).' Fig. 3 shows that the presented tnethod of detertninalion of cost-effeetiveness is also possible with other data and thus useful for other situatiotis atid countries, ln this figute the cost ratio is chosen to be 2 10 3. ll is clear that the slope ofthe lines for adhesixe bridges has decreased. As a resttlt the lities for both Ihe atilerior and posterior bridges are tiow loeated DURABILITY 20.
DURABILITY
1/3 «
COST
Eig. /. CTraphical representation oi' the relationship of dnrability and cost for a certain con.stani cost-cflectivcncss (cost-benefit plot).
«
COST
Fig. 2. Durabilitx data for adhesive bridges and conventional bridges projected in the schematic cost-bencHt plot lor a cost ratio of 1 to .V 1; assessed 50" n siirvixal of anterior adhesive bridges, 2: reported 50" o survival of conventional bridges, 3; stirvival of anterior adhesive bridges, 4: breakeveti point for equal cost-effcctivcncss. .A: anterior adhesive bridges, C: conventional bridges.
282
CREtJGF.RS AND K A Y S I Z R
eratute (II), Another complication with posterior adhesive bridges is that the 20. evaluated popttlations were relatively small while the observation periods were relatively short. This tneans that the calculation of the cost-effectiveness of posterior adhesive bridges shottld be tnade 10. with extretne care. The data of posterior adhesive bridges are therefore excluded frotn our calculations. However, as tnentioned above, there are indications that the durability of posterior adhesive bridges is less than the durability of anterior adhesive bridges (8). The informa« COST tion about the lifetitne expectations of F'ig. 3. Durability data for adhesive bridges and conventional bridges projected in the scheanterior adhesive bridges indicates better matic cost-bcnelu plot for a cost ratio of 2 to cost-effectivcness for the situation in the 3. 1; assessed 50'!^. survival of anterior adhesive Netherlands. Allliough there are sotne bridges, 2: reported 5O'^i survival of convenlitnitations due to some sitnplifications, tional bridges, 3: survival of anterior adhesive bridges, 4: breakeven point for equal cost-efthe principles of the method retnains fectiveness. A: anterior adhesive bridges, C; valid in our opinion. conventional bridges. It is important to note that the costeffectiveness calculation of adhesive in the fteld of lower cost-effectiveness. bridges, as presented in this study, is only However, the estimated confidence inter- a part ofthe trealment itnplications. The vals for anterior adhesive bridges (95'V!i different indicatiotis for the various reinterval; 68--80'^ survival after 7.5 yr constructiotis and the cotnplcxity of the (10)) may indicate the need for a correc- Iteatment also have an itnpacl on the tion when tnore long-term data beeotne cost and benefit of a treattnent. available. Another consideration in the cost-betiDespite Ihe fact that a nutnber of fae- efit analysis is the oral situation after tors in the cost benefit analysis are un- failure ofthe bridge, which is in favor of known or difficult to compare, it may be Ihe adhesive bridge. Due to biological concluded that the cost-effectiveness of effects, especially caries, the "rest-valtte" adhesive bridges is in general cotnparable of the abuttnent teeth may be substanto the cost-effectiveness of conventional tially decreased after failure of a convenbridges. In teality the cost-benefit plots tional bridge, tesulling in Ihe fabrication may be tnore complicated as the lifetimes of a new bridge, if this is possible at all. might not be directly ptoporlional wilh In ihis atialysis the survival of adhesive time. As a result of this, the value of the bridges was determined from the number cost-effectiveness (which is dependent on of detached bridges (8, I 1). Since adhethe durability data) can also show llueluations. Due to factors as tnaterial fatigue sive bridges are relatively easy to rebond the survival rates, as expressed in a per- atul loosening does not automatically centage per yeat\ tnay increase substan- lead to loss of the reconstruclion, the tially after 5, 10 or 20 yr (15), Moreover calculated survivals may be an undereslithe durability expectation is in reality not matioti ofthe number of bridges in funca single line but an area. Durability data tioti, tesulting in a too negative image. of adhesive bridges are still restricted to However, there are indications that the short- and mid-term studies. This means survival of tebonded bridges is not as that the assessment of the durability has good as the survival of originally bonded to be based on survival data, ineluding adhesive bridges (9, 18). confidence intervals. The Nijtnegen adWith respect to the durability of the hesive bridge trial was used for this pur- conventional bridges, the data reported pose because the reports of this study are divergent. The results of durability provided confidence intervals. With re- studies are expressed in a failure percenspect to the durability data of posterior tage per year, indicating indirectly the adhesive bridges it has to be tnenlioned survival pereentage, Howevet, many that there is substatitial variation in the sttidies do not give clear infortnation resurvival percentages presented in the lit- garding the quality of the surviving DURABILITY
populatioti, which may tesult iti a t o o positive image (12, 13) Esthetics and subjective comfort are also factors of benefit. These factors are difficult to quantify for populations of palieiits and therefore diffieult to include in calculations for cost-effeetivetiess However, in Ihis sludy the esthetic result and oral comfort of the evaluated restorations were eonsidered to be tnore o r less similar. There are other factors vvhiel-i were not iticluded, stich as the social costs for the patient (the titne needed to see the dentist) and psychological aspects (fear for dislodgetneiit, patients' satisfaction). More researeh needs to be dotie on these social and psychological ditnen, sions.
References t. CRliUGtiRS NH.I. Ctiniccd pcrftniiiaiiee of adhesive bridges. Thesis, I'tirosound liV Nijmegen, 19X7. 2. IVlAt(iNi:i.i.o Cl'. Adhi'isivprotlietik Klitij.. sclie und materiatkuiidticlie Aspekte. Berlin; Qtiintcssenz, 1991. 3. Vi:K/.i.ii)t:N CWG.IM, C't
