a cost-effectiveness analysis of implant-supported...

A cost-effectiveness analysis of implant-supported removable partial dentures in the mandible.

Student: Jamila Ross (1741179) Supervisors: Prof. dr. M.S. Cune, mw. dr. T.L. Feenstra, mw. drs. C. Jensen - Louwerse

Date: June 25th, 2014 Research period: February 10th – July 4th, 2014

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SUMMARY Supporting a Removable Partial Denture (RPD) with implants can be beneficial to the many shortcomings associated with conventional RPD treatment. However it is also quite likely to increase treatment costs. The aim of this study was to conduct a cost-effectiveness analysis comparing conventional RPD and Implant Supported Removable Partial Denture (ISRPD) treatment in patients with a bilateral free-ending situation in the mandible.

Eleven patients were included, a new RPD was made and implant support was provided 3 months later. Opportunity costs and costs based on the national tariff structure where determined and compared to 3 outcome measures: oral health related quality of life measured using the OHIP-NL49, a chewing ability test (Mixing Index) and perceived general health (SF-36) which was subsequently converted into Quality-adjusted Life Year’s (QALY’s). Outcome measures where determined at 3 moments in time: baseline (To), after having worn a newly made conventional RPD for 3 months (T1) and 3 months after the provision of implant support to the RPD (T2).

Results strongly depend on choice of outcome measure. When SF-36 is used as an outcome measure no incremental effect and thus added value was found. When MI or OHIP are used as outcome measures implant supported RPD’s provide better outcomes. A minimal importance difference (MID) is only known for OHIP, making clinical relevance of MI difficult to determine.

Considering the clinical relevance of the gain in oral health related quality of life, supporting a RPD with implants is cost effective when a monetary threshold exceeding than €130 per OHIP point gained is adopted. SAMENVATTING Het ondersteunen van een uitneembare partiële prothese (RPD) met implantaten kan gunstig zijn voor de vele tekortkomingen gerelateerd aan een conventionele RPD behandeling. Daarentegen zullen de kosten van de behandeling zeer waarschijnlijk ook stijgen. Het doel van deze studie was om de kosten-effectiviteitsanalyse uit te voeren waarbij de kosten en de effecten van een conventionele RPD behandeling en een door implantaten ondersteunde partiële prothese (ISRPD) behandeling bij patiënten met een bilaterale vrij-eindigende situatie in de mandibula met elkaar vergeleken werden. Elf patiënten werden geïncludeerd waarbij een nieuwe RPD werd vervaardigd. Deze werd 3 maanden later door 2 implantaten ondersteund. Opportuniteitskosten en kosten op basis van de door de Nederlandse Zorg Autoriteit vastgestelde tarieven werden bepaald en vergeleken met 3 uitkomstmaten: mondgezondheid gerelateerde kwaliteit van leven gemeten met de OHIP-NL49, een kauwfunctietest (Mixing Index, MI) en de ervaren algemene gezondheid (SF-36) welke vervolgens werd omgezet in Quality-adjusted Life Years (QALY's). Uitkomstmaten werden gemeten op 3 momenten in de tijd: de nulmeting (T0), na een nieuw gemaakte conventionele RPD te hebben gedragen voor 3 maanden (T1) en 3 maanden na het ondersteunen van de RPD met implantaten (T2). De gevonden resultaten zijn sterk afhankelijk van de gekozen uitkomstmaat. Wanneer SF-36 wordt gebruikt als uitkomstmaat zijn er geen positieve effecten en is er dus geen toegevoegde waarde aantoonbaar. Wanneer MI of OHIP worden gebruikt als uitkomstmaten bied een ISRPD betere resultaten. Een drempelwaarde voor klinische relevantie is alleen bekend voor de OHIP meetresultaten, in tegenstelling tot MI, waardoor klinische relevantie van de toename in kauwfunctie moeilijk te bepalen is. Gelet op de klinische relevantie van de winst in mondgezondheid gerelateerde kwaliteit van leven, is het ondersteunen van een RPD met implantaten kosteneffectief wanneer men bereid is meer dan € 130 per gewonnen OHIP punt te investeren.

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TABLE OF CONTENTS INTRODUCTION ......................................................................................................................................... 4

MATERIALS & METHODS ........................................................................................................................... 4 TREATMENT COSTS ......................................................................................................................................... 5 OUTCOME MEASURES ..................................................................................................................................... 6 COST-EFFECTIVENESS .................................................................................................................................... 6 STATISTICAL ANALYSIS .................................................................................................................................... 7

RESULTS .................................................................................................................................................... 7

DISCUSSION ............................................................................................................................................ 11

CONCLUSION ........................................................................................................................................... 13

REFERENCES ............................................................................................................................................ 14

APPENDIXES ............................................................................................................................................ 17 ANNEX 1: UITEENZETTING KOSTENBEPALING ............................................................................................ 17 ANNEX 2: UITKOMSTMATEN ....................................................................................................................... 20 ANNEX 3: ORIGINELE DATA UITKOMSTMATEN ........................................................................................... 22

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INTRODUCTION From a functional perspective not all teeth that are lost need replacement. A new occlusal equilibrium can generally be established, in which case adequate oral function is maintained. 1 In case of adverse conditions or when many teeth are missing, replacement therapy may be indicated. Dental rehabilitation may involve the provision of conventional removable partial dentures (RPDs) but their merits are modest as patients frequently complain from a lack of stability and retention. Studies show that within 5 years, approximately 25% of all RPDs needed replacement or where not being worn. This number increases to 50% in 10 years. 2-4 Supporting such a RPD with implants can be beneficial, increasing stability, retention and chewing ability and improving patient comfort in general. 5-7 The use of unaesthetic clasps can frequently be avoided. 8 However, providing implant support to a conventional RPD is quite likely to increase treatment costs. In recent years the rise in health care costs has been a controversial topic in the public debate. Whilst the share of health care costs in the gross domestic product (GDP) of the Netherlands in the year 2000 was only 9 %, in 2012 it rose to 13 %. It is predicted that if health care costs continue to grow at this rate, its share will be 31 % of the GDP in the year 2040. According to the Dutch Bureau for Economic Policy Analysis (Centraal Planbureau), health care costs rise faster than the country’s economic growth. This cannot merely be explained by the fact that the population is aging. Technological advances and increased treatment possibilities are thought to play an important role in the increasing demand for care as well. 9 This increasing demand for care, the limited funds available and the intent to maintain affordable health care for everyone over the years to come requires an efficient use of available resources.10 When several treatment options are available, both their documented or presumed effectiveness and their (additional) costs should be considered when favoring one treatment over the other. A cost-effectiveness analysis can provide insight into whether the more costly treatment option offers sufficient added value to the patient to justify its application. Currently, in the Dutch setting, economic evaluation is mainly important for new pharmaceuticals, and still has a limited weight in reimbursement decisions. 11 In dentistry economic appraisal is not yet widely used. It was suggested that in the Netherlands this can be explained in part by the fact that dental care is usually not paid for by the national health insurance scheme, but mainly (circa 73 % in 2011) through private insurance or out of pocket. 12,13 In recent years the use of economic evaluation in oral health care received increasing attention and it is being applied more frequently. Zitzmann et al. for example, examined the cost-effectiveness of implant overdentures and find that over an assumed time horizon of 10 years implant treatment becomes cost-effective with implant-retained overdentures being the treatment of choice, if the patient is willing to pay at least CHF 3800 for a Quality-adjusted Prosthesis Year gained. 14 Studies like this can aid dentists and patients alike to make treatment decisions that use patients’ funds in the most effective way.15,16 No information addressing the anticipated benefits of implant-supported RPDs (ISRPDs) in relation to the expected extra costs was found during literature search. The aim of this study is to conduct a cost-effectiveness analysis comparing conventional RPD and ISRPD treatment in patients with a bilateral free-ending situation in the mandible, also referred to as a mandibular Kennedy class I mutilation.17

MATERIALS & METHODS This pilot study is part of an ongoing investigation conducted by drs. C. Jensen, at the department of Fixed and Removable Prosthodontics, Center for Dentistry and Oral Hygiene at the University Medical Center of Groningen, the Netherlands. Thirty patients with a full upper denture and complaints regarding their bilateral free-ending mandibular RPD were included. The inclusion and exclusion criteria are summarized in table 1. A new RPD was made and implant support was provided 3 months later. Patient based and functional outcome measures were among the

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parameters of evaluation collected at several moments in time, with an endpoint at 3 months of function with implant support. At the time of preparation of this MSc thesis, eleven patients had completed the study and the data from their files were used. Table 1: Inclusion and exclusion citeria.

Inclusion criteria: - the patient is ≥ 18 years of age; - the bone volume distal from the most posterior abutment teeth should allow the placement of

implants with a minimum length of 8 mm and minimum diameter of 3.3 mm; - the patient has complaints regarding his bilateral, free-ending RPD in the mandible and has a

complete denture in the maxilla; - the patient is capable of understanding and giving informed consent.

Exclusion criteria: - medical and general contraindications for the surgical procedures; - a history of local radiotherapy to the head and neck region; - previous implant loss; - incapability of performing basal oral hygiene measures as a result of physical or mental

disability; - decreased masticatory function due to physical disability; - active, uncontrolled periodontal pathology of the remaining dentition.

Treatment costs The cost effectiveness study was performed from a payer perspective. This would usually be a private person but could also be a health care insurer. Hence, health care costs are included and valued at their market prices using tariffs. 18 For better comparison to treatments that are reimbursed by public insurance, in addition a cost-effectiveness analysis from a societal perspective was performed. This analysis estimated costs by calculating the, opportunity costs of the different procedures. That is, the value of a procedure was assessed as the value of the best alternative use that could be made of the resources involved in the procedure. In practice, this implies assessing time costs of professionals involved and using the Dutch costing manual and the standard salary scales of the Collective Labor Agreement (CAO) to value this (table 2). 19,20 Because all resource use occurs at the same point in time (2013) discounting will not provide additional insight on the costs. A detailed description and the raw dataset is presented in annex 1.

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Table 2: Type of costs, units and unit price for Removable Partial Dentures (RPD) and Implant Supported Removable Partial Dentures (ISRPD) in the Netherlands (price level 2013).

Type of costs Resource use RPD

Resource use ISRPD

Unit Unit price (€)

Labor costs Oral and Maxillofacial Surgeon

- 65 ±10% Minute € 1.88

Labor costs assistent Oral and Maxillofacial Surgeon

- 90 ± 10% Minute € 0.54

Labor costs dentist* 165 ± 10% 240 ±10% Minute € 2.76 * Includes costs for assistent and practice costs. Time costs assesd using Cost manual Hakkaart-van Royen standard salary scales of Collective Labor Agreement 2013-2015 (CAO UMCs). See annex 1.

Outcome measures Three outcome measures were used as effect parameters. The OHIP-NL49 is a validated questionnaire measuring various domains of oral health related quality of life (OHRQoL). 21,22 A chewing ability test (Mixing Index) was carried out as an objective measure of oral function and a short-form health survey measured perceived general health (SF-36). 23-25 The SF-36 dataset was subsequently converted into Quality-adjusted-life-year’s (QALY’s) using the SF-6D excel scoring program provided by the University of Sheffield and assuming that the measured quality of life would continue for a year. 26 A more detailed description of the outcome measures is presented in annex 2. Patients were asked to complete both questionnaires and perform the chewing ability test at three moments in time: baseline (To), after having worn a newly made conventional RPD for 3 months (T1) and 3 months after the provision of implant support to the RPD (T2) (Figure 1).

Figure 1. Timeline.

Cost-effectiveness The incremental cost-effectiveness ratio (ICER) represents the difference in costs divided by the difference in effects between the two treatment strategies and is expressed by the following formula: 𝒄𝒐𝒔𝒕𝒔 𝑨!𝒄𝒐𝒔𝒕𝒔 𝑩

𝒆𝒇𝒇𝒆𝒄𝒕𝒔 𝑨!𝒆𝒇𝒇𝒆𝒄𝒕𝒔 𝑩 = ∆𝑪

∆𝑬

Here, costs A are the average costs per patient for ISRPD treatment and costs B are the average costs per patient for conventional RPD treatment. Effects A and B are the average effects per patient for ISRPD and RPD treatment respectively. The ICER was calculated for the two treatment strategies, both from a payer perspective and from a societal perspective and was determined for the three outcome measures mentioned before. It describes the costs per additional unit of effect for the ISRPD treatment compared to a conventional RPD treatment.

TO. Baseline. Data

collection + diagnostic x-

rays.

Implantation

3 months after implantation.

start production new RPD

5 monts after implantation,

new RPD placed.

T1. Data collection

after wearing new RPD for

3 months.

T2. Data collection

after wearing ISRPD for 3

months.

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Statistical Analysis To analyze the data Microsoft Office Excel (2011) was used. Uncertainty around the outcome measures was estimated using bootstrapping, generating 5000 replications of the original data set and using interquartile ranges to express uncertainty (2.5th and 97.5th percentile). To determine uncertainty around the opportunity costs, minimum and maximum time requirements were assumed by adding or subtracting an uncertainty range of 10% from the established total time requirements of the professionals. A uniform distribution of actual time was then assumed within this range and used to estimate the variation in costs over individual patients. No uncertainty was determined around the costs based on the tariff structure, because these are fixed values. To visualize the uncertainty in costs and effects a scatter plot of these simulated incremental costs and effects is displayed in the cost-effectiveness plane.

RESULTS Clinical outcomes Eleven patients were included and the group comprised of 9 men and 2 women. The mean age of the patients was 62.0 ± 6.1 years. The mean improvement in chewing ability as expressed by the MI, after bootstrapping and correcting by multiplying with -1 so that a lower score constitutes a better result, was 1.44. The mean gain in oral health related quality of life, after bootstrapping and correcting by multiplying with -1 so that a lower score constitutes a better result, was 11.46. A small mean decrease in QALYs was measured, i.e. -0.01 (Table 3). The raw, original data before bootstrapping can be reviewed in annex 3. Table 3: Mean effects after bootstrapping for the Oral Health Impact Profile (OHIP), for the Mixing Index (MI) and for the Quality Adjusted Life Years (QALY).

OHIP (95% IQR)

MI (95% IQR)

QALY (95% IQR)

T1: RPD 24.59 (17.18 to 31.64)

19.76 (19.01 to 20.60)

0.81 (0.74 to 0.86)

T2: ISRPD 13.13 (6.91 to 21.00)

18.32 (17.82 to 18.90)

0,80 (0.74 to 0.86)

Δ 11.46 (7.09 to 15.81)*

1.44 (0.66 to 2.30)*

-0.01 (-0.04 to 0.03)

* Corrected by multiplying with -1 so that a lower score constitutes a better result. RPD: Removable Partial Denture, ISRPD: Implant Supported Removable Partial Denture. Treatment costs The mean total opportunity costs were € 980 (95% IQR 969 to 1000) for the conventional RPD treatment and € 2.470 (95% IQR 2439 to 2501) for the ISRPD treatment. The total costs derived from the national tariff structure were € 850 for the conventional RPD treatment and € 2.610 for the ISRPD treatment. The breakdown of the costs is presented in table 4.

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Table 4: Mean opportunity costs and costs based on tariff structure for Removable Partial Dentures (RPD) and Implant Supported Removable Partial Dentures (ISRPD).

RPD ISRPD Opportunity costs Labor costs dentist* € 450 ± 10% € 660 ± 10% Labor costs Oral and Maxillofacial Surgeon (total + 42%)*

€ 240

Labor costs Oral and Maxillofacial Surgeon € 120 ± 10% Labor costs assistant Oral and Maxillofacial Surgeon

€ 50 ± 10%

Invoice laboratory work (excl. VAT) € 530 € 1030 Purchase price implants and abutments (excl. VAT) € 530 Total opportunity costs (95% IQR) € 980 (969 to 1000) € 2.470 (2439 to 2501) Costs (tariff)** Labor costs dentist € 320 € 320 Labor costs Oral and Maxillofacial Surgeon € 720 Invoice laboratory work (excl VAT) € 530 € 1040 Purchase price implants and abutments (excl VAT) € 530 Total costs (tariff) € 850 € 2610 * Cost manual Hakkaart-van Royen standard salary scales of Collective Labor Agreement 2013-2015 (CAO UMCs) ** www.nza.nl Cost-effectiveness. The incremental cost ratios for the 2 treatment options and corresponding outcome measures (OHIP, MI, QALY’s) are presented in table 5 and figure 2 till 7. The ICER for the outcome measure OHIP using the opportunity costs was €130, this means that per OHIP point gained an additional €130 has to be invested. The ICER for the outcome measure OHIP using the tariff structure based costs was €150, this means that per OHIP point gained an additional €150 has to be invested. The ICER for the outcome measure MI using the opportunity costs was €1060, this means that per MI point gained an additional €1060 has to be invested. The ICER for the outcome measure MI using the tariff structure based costs was €1230, this means that per MI point gained an additional €1230 has to be invested. The ISRPD had higher costs and worse QALY’s than the RPD, thus an ICER was not determined. Table 5: Incremental costs ratios (ICER) for Removable Partial Dentures (RPD) and Implant Supported Removable Partial Dentures (ISRPD) using the Oral Health Impact Profile (OHIP), the Mixing Index (MI) and the Quality Adjusted Life Years (QALY) as outcome measures.

Type of Costs Effect Incremental costs (€)**

Incremental effects*

ICER**

Opportunity costs OHIP € 1490 11,45 130

MI € 1490 1,43 1060 QALY € 1490 -0,01 N/A

Costs (tariff) OHIP € 1760 11,45 150 MI € 1760 1,43 1230 QALY € 1760 -0,01 N/A

* Displayed numbers are rounded to two decimals, full numbers were used for analysis. ** Displayed numbers are rounded to tens.

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Figure 2: Results of cost-effectiveness analysis based on the opportunity costs and using the Oral Health Impact Profile (OHIP) as outcome measure. The calculated incremental cost-effectiveness ratio (ICER) was €130 meaning that per OHIP point gained an additional €130 has to be invested.

Figure 3: Results of cost-effectiveness analysis based on the opportunity costs and using the Mixing Index (MI) as outcome measure. The calculated incremental cost-effectiveness ratio (ICER) was € 1060 meaning that per MI point gained an additional € 1060 has to be invested.

-2000

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Figure 4: Results of cost-effectiveness analysis based on the opportunity costs and using Quality Adjusted Life Years (QALY) as outcome measure. The incremental cost-effectiveness ratio (ICER) was not determined since Implant Supported Removable Partial Dentures (ISRPD) had higher costs and worse QALYs than conventional treatment with a Removable Partial Dentures (RPD).

Figure 5: Results of cost-effectiveness analysis based on the costs based on the national tariff structure and using the Oral Health Impact Profile (OHIP) after as outcome measure. The calculated incremental cost-effectiveness ratio (ICER) was €150 meaning that per OHIP point gained an additional €150 has to be invested.

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Figure 6: Results of cost-effectiveness analysis based on the costs based on the national tariff structure and using the Mixing Index (MI) as outcome measure. The calculated incremental cost-effectiveness ratio (ICER) was €1230 meaning that per MI point gained an additional €1230 has to be invested.

Figure 7: Results of cost-effectiveness analysis based on the costs based on the national tariff structure and using Quality Adjusted Life Years (QALY) as outcome measure. The incremental cost-effectiveness ratio (ICER) was not determined since Implant Supported Removable Partial Dentures (ISRPD) had higher costs and worse QALYs than conventional treatment with a Removable Partial Dentures (RPD).

DISCUSSION When applying economic evaluation in dentistry, specifically in prosthodontics, several

difficulties remain. Attempts at determining the costs of treatment vary widely. 27 The same can be said for outcome measures. A lack of a common outcome measure makes comparison of different treatments complicated. 28 In addition assessing the value that a patient derives from his dental treatment is difficult and the dental profession has not yet reached consensus on how to measure this added value. 29 Biological, clinical and functional outcome measures are necessary, but equally important are patient’s improvements in oral health status, satisfaction, oral and psychological function, self-esteem and quality of life considerations. 28 Several attempts have been made to introduce a universal outcome measure for dentistry. For example Zitzmann et al. use Quality-adjusted Prosthesis Years, which is defined as the number of years of service of a prosthesis adjusted by quality. 14,30 Unfortunately these attempts are not yet broadly used in literature. In order to overcome this problem, this study uses different outcome measures to determine cost-effectiveness from different perspectives. By using the OHIP as a subjective measure for patient

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perceived oral health quality, the MI as a objective measure of chewing ability and the QALY as a measure for perceived general health quality, a wide range of outcomes is covered. This study shows that when assessing the cost effectiveness from the OHIP or MI perspective the additional costs for the ISRPD treatment do provide an additional effect, with ICER’s in the northeast quadrant of the cost effectiveness plane. Unlike assessing the cost effectiveness from the QALY perspective, where the ICER has moved towards the northwest quadrant of the cost effectiveness plane indicating additional cost but no incremental effect and thus seems to favour RPD treatment over ISRPD treatment. These varying results emphasize the leverage of outcome measure choice when conducting a cost-effectiveness analysis.

Although the number of patients included in this study is small and incremental QALY scores are generally small, the minuscule difference in QALY score between the two treatment options is noteworthy.31SF-36 as an effect measure in prosthodontic treatment, as the one described in this study, is questionable since it has not always proved to be able to discriminate between clinically distinct groups and thus may not be sensitive enough for this purpose. 32 However the validity of the SF-36 questionnaire is often described and it can therefore be assumed to measure what it claims to measure. This indicates that no changes to perceived general health can be attributed to supporting a conventional RPD with implants. 25 This underlines the aforementioned importance of outcome measure choice when economic evaluation is used in dentistry. It also raises doubt regarding the manner in which continuous effort is invested in associating dental issues in all fields of study to overall general health matters. A clear improvement of quality of life can be seen after prosthodontic rehabilitation in patients surgically treated for malignancies in the oral cavity resulting in severe compromised oral function and/or esthetics. 33 However, an overestimation of desired results might occur when less intrusive dental health issues are sought to influence perceived general health and overall quality of life.

The mean reduction of 11.45 point in OHIP-NL49 is consistent with results found by Gates et al. who reported an OHIP-49 reduction of 11.8 points and several other retrospective studies and case reports. 5-7,34 John et al. determined a minimal importance difference (MID) of 6 points (95% CL, 2 to 9) for OHIP use in dentistry. 35 The MID was defined as “the smallest difference in score in the domain of interest which patients perceive as beneficial and which would mandate, in the absence of troublesome side effects and excessive cost, a change in the patient’s management.” As suggested in the same study this MID can be used to approach clinical relevance of changes in perceived oral health. This indicates that the reduction of 11.45 OHIP points in this study, leads to a clinically relevant change in oral health related quality of life. When assessing the clinical relevance of the incremental effects of the MI there is no such thing as a MID or other threshold available. This makes interpretation of the observed reduction in MI points difficult. When considering loss of chewing ability after surgery in patients with squamous cell carcinoma of the tongue and/or floor of mouth an average reduction of the MI score by 2 points is statistically significant (p = .045). 36 Although this gives a slightly better understanding of the outcome measure it does not provide a threshold to determine whether the results of this study are clinically relevant.

Because of the retrospective character of this study, resource use was determined by interviewing the professionals involved. Timing each individual procedure after which an average treatment time can be determined could assess a more accurate approach to resource use and is advisable for prospective studies.

To decide if an intervention is cost effective and thus offers “good” value for money, the ICER should be compared to a specified monetary threshold as done by Zitzmann et al. 14 This threshold represents the maximum amount of money that a decision-maker is willing to pay for an additional effect. 37 In the present study the height of the threshold was not examined and standardized value’s are not available, so this could not be determined. An effort to set such a threshold (range) would complement a future study.

Finally, another important factor in assessing cost-effectiveness is the time horizon that is adopted. This study analyzed a short time horizon, only examining the treatment costs and effects

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during the timeline of the initial investigation conducted by drs. C Jensen - Louwerse. Hence, it only took initial costs and effects in to account. Aftercare costs, other future expenses and the sustainability of the prosthetic solution were not taken into consideration and this would make a valuable addition for further studies. This because large, long term benefits that might be expected when supporting a RPD with implants may positively influence the ICER. As in medicine, these longitudinal analyses are complex and difficult to implement. 28 These issues combined with the difficulties referred to above is why further collaboration with health economists to guide future research is advised.27An increased proficiency in health care economics amongst dental researchers could favor this collaboration.

CONCLUSION Depending on the choice of outcome measure and monetary threshold implant supported RPD treatment can be considered cost effective. When SF-36 is used as an outcome measure to determine the impact on general health no incremental effect and thus added value was found. When outcomes measures are chosen that are dentistry specific, such as MI or OHIP, the additional costs of implant supported RPD’s provide better outcomes. Although improvement of chewing ability is seen, a minimal importance difference (MID) for MI is not available and it is therefore not possible to determine whether the gain in chewing ability is clinically relevant and thus offers extra value for money spent. Considering the clinical relevance of the gain in oral health related quality of life, supporting a RPD with implants is cost effective when a monetary threshold exceeding €130 per OHIP point gained is adopted.

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22. van der Meulen M, Lobbezoo F, John M, Naeije M. Oral health impact profile. meetinstrument voor de invloed van de mondgezondheid op de levenskwaliteit. Ned Tijdschr Tandheelkd. 2011;134(118).

23. Kamiyama M, Kanazawa M, Fujinami Y, Minakuchi S. Validity and reliability of a self-implementable method to evaluate masticatory performance: Use of color-changeable chewing gum and a color scale. Journal of prosthodontic research. 2010;54(1):24-28.

24. Speksnijder CM, Abbink JH, Van Der Glas HW, Janssen NG, Van Der Bilt A. Mixing ability test compared with a comminution test in persons with normal and compromised masticatory performance. Eur J Oral Sci. 2009;117(5):580-586.

25. Aaronson NK, Muller M, Cohen PD, et al. Translation, validation, and norming of the dutch language version of the SF-36 health survey in community and chronic disease populations. J Clin Epidemiol. 1998;51(11):1055-1068.

26. McCabe C, Brazier J, Gilks P, et al. Using rank data to estimate health state utility models. J Health Econ. 2006;25(3):418-431.

27. Bassi F, Carr AB, Chang T, et al. Economic outcomes in prosthodontics. Int J Prosthodont. 2013;26(5).

28. Lewis DW. Optimized therapy for the edentulous predicament: Cost-effectiveness considerations. J Prosthet Dent. 1998;79(1):93-99.

29. Walton T, Layton D. Cost satisfaction analysis: A novel patient‐based approach for economic analysis of the utility of fixed prosthodontics. J Oral Rehabil. 2012;39(9):692-703.

30. Sendi PP, Palmer AJ, Marinello CP. Health state utilities in dentistry: A review. Acta Medicinae Dentium Helvetica. 1997;2(10):243-248.

31. Wisløff T, Hagen G, Hamidi V, Movik E, Klemp M, Olsen JA. Estimating QALY gains in applied studies: A review of cost-utility analyses published in 2010. Pharmacoeconomics. 2014:1-9.

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32. Allen PF, McMillan AS, Walshaw D, Locker D. A comparison of the validity of generic‐and disease‐specific measures in the assessment of oral health‐related quality of life. Community Dent Oral Epidemiol. 1999;27(5):344-352.

33. Korfage A, Schoen PJ, Raghoebar GM, et al. Five‐year follow‐up of oral functioning and quality of life in patients with oral cancer with implant‐retained mandibular overdentures. Head Neck. 2011;33(6):831-839.

34. Grossmann Y, Nissan J, Levin L. Clinical effectiveness of implant-supported removable partial dentures—a review of the literature and retrospective case evaluation. Journal of Oral and Maxillofacial Surgery. 2009;67(9):1941-1946.

35. John MT, Reißmann DR, Szentpétery A, Steele J. An approach to define clinical significance in prosthodontics. Journal of Prosthodontics. 2009;18(5):455-460.

36. Speksnijder CM, van der Bilt A, Abbink JH, Merkx MA, Koole R. Mastication in patients treated for malignancies in tongue and/or floor of mouth: A 1‐year prospective study. Head Neck. 2011;33(7):1013-1020.

37. Fenwick E, Marshall DA, Levy AR, Nichol G. Using and interpreting cost-effectiveness acceptability curves: An example using data from a trial of management strategies for atrial fibrillation. BMC Health Services Research. 2006;6(1):52.

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APPENDIXES

Annex 1: Uiteenzetting kostenbepaling Het in kaart brengen van de kosten is gedaan aan de hand van de richtlijnen uit de Handleiding voor kostenonderzoek geschreven in opdracht van het College voor Zorgverzekeringen. 19 Om de kosten eenheden te identificeren is gestart met het volledig in kaart brengen van beide behandeltrajecten (zie tabel 1). Tabel 1: Overzicht behandeltrajecten: conventionele behandeling met behulp van een Removable Partial Denture (RPD) en Implant Supported Removable Partial Denture (ISRPD).

Behandelstap RPD ISRPD 1 Diagnostiek tijdens probleem

gericht consult. Diagnostiek tijdens probleem gericht consult.

2 Intake consult implantologie door kaakchirurg. Incl. OPT, Botvolume bepaald a.d.h.v. klinisch onderzoek i.c.m. röntgenologisch onderzoek. Zo nodig CBCT, afdrukken voor vervaardigen boorsjabloon.

3 Techniek: vervaardigen boorsjabloon. 4 Plaatsen implantaten Straumann SP (2x),

onder lokale anesthesie. Door kaakchirurg.

5 Nazorg: 2wk na impl hechtingen verwijderen, aanpassen frame met softliner, vervaardigen OPG. Door tandarts.

6 12wk impl vrijleggen + plaatsen healing abutments. Door kaakchirurg.

7 Begin afdrukken BK & OK, d.m.v. alginaat.

Begin afdrukken BK & OK, d.m.v. alginaat.

8 Techniek: uitgieten afdrukken en montage in articulator. Ontwerp frame m.b.v. surveyor. Vervaardigen individuele lepel.

Techniek: uitgieten afdrukken en montage in articulator. Ontwerp frame m.b.v. surveyor. Vervaardigen individuele lepel.

9 Steunen en eventuele doorvoeren inslijpen bij patiënt en zo nodig vorm pijler elementen wijzigen d.m.v. composiet opbouw. Afdruk m.b.v. individuele lepel. OK & BK Provil®. Uitzoeken van de vorm, kleur en materiaal van elementen.

Steunen en eventuele doorvoeren inslijpen bij patiënt en zo nodig vorm pijler elementen wijzigen d.m.v. composiet opbouw. Afdruk m.b.v. individuele lepel. OK & BK Provil®. Uitzoeken van de vorm, kleur en materiaal van elementen.

10 Techniek: uitgieten individuele afdrukken. Vervaardigen kunststof registratieplaten met waswallen voor BK, in OK frame in metaal met waswal als registratie plaat.

Techniek: uitgieten individuele afdrukken. Vervaardigen kunststof registratieplaten met waswallen voor BK, in OK frame in metaal met waswal als registratie plaat.

11 Relatiebepaling m.b.v. waswallen. Uitgangspunt is de VP. BK: registratieplaat waswal OK: frame metaal.

Relatiebepaling m.b.v. waswallen. Uitgangspunt is de VP. BK: registratieplaat waswal OK: frame metaal.

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12 Techniek: monteren in articulator. Opstellen in was OK en BK.

Techniek: monteren in articulator. Opstellen in was OK en BK.

13 Passen van het frame met elementen in was. Beoordeling relatiebepaling, occlusie en articulatie. Beoordeling esthetiek en fonetiek.

Passen van het frame met elementen in was. Beoordeling relatiebepaling, occlusie en articulatie. Beoordeling esthetiek en fonetiek.

14 Techniek: Afmodelleren, Persen, Remounten, Reoccluderen, Afwerken.

Techniek: Afmodelleren, Persen, Remounten, Reoccluderen, Afwerken.

15 Plaatsen frame, controle pasvorm, occlusie & articulatie en beethoogte. Kiezen mate van retentie.

Plaatsen frame, controle pasvorm, occlusie & articulatie en beethoogte. Kiezen mate van retentie.

16 1e nazorg na 2 wk: bepalen vervolg traject.

1e nazorg na 2 wk: bepalen vervolg traject.

Kosten bepaling op basis van tarieven Dit zijn de kosten zoals deze betaald worden door de patiënt of zijn particuliere verzekering. Hiervoor is gebruik gemaakt van de tariefcode’ s voor de tandheelkundige zorg zoals vastgesteld door de NZA geldig in 2013. Vervolgens is daar de (inkoop)prijs (excl. BTW 6%) voor de implantaten en abutments die doorberekend wordt aan de patiënt bij opgeteld en is de factuur (excl. BTW 21%) van het tandtechnisch laboratorium opgenomen in de totale kosten. Kosten bepaling op basis van afgeleide kosten Voor het zelf afleiden van de kosten is een tijdstarief voor de tandarts berekend op basis van het inkomsten- en praktijkkosten (incl. materiaalkosten) bestanddeel van de NZA. Vervolgens is op basis van het aantal patiënt gerelateerde uren per jaar een uur- en een minuuttarief berekend. Voor de kaakchirurg en zijn ondersteunend personeel is, volgens de richtlijnen uit de handleiding voor kostenonderzoek, gekeken naar het brutosalaris op basis van het CAO, waar respectievelijk 35% en 39% aan aanvullende personeelskosten bij opgeteld zijn. 19,20 Vervolgens is op basis van het aantal patiënt gebonden uren per jaar een uur- en minuuttarief opgesteld (tabel 2 t/m 5). Tabel 2: Type kosten, eenheden en eenheidsprijs voor een Removable Partial Dentures (RPD) en Implant Supported Removable Partial Dentures (ISRPD) in the Nederland (prijs niveau 2013).

Type kosten Gebruik van middelen RPD

Gebruik van middelen ISRPD

Eenheid Eenheidsprijs (€)

Kosten kaakchirurg - 65 Minuut 1,88 Kosten ondersteunend personeel kaakchirurg

- 90 Minuut 0,54

Kosten tandarts* 165 240 Minuut 2,76 * overige praktijk kosten inbegrepen, o.a. materiaal kosten en personeel. Eenheidsprijs berekend op basis van de handleiding kostenonderzoek van Hakkaart-van Royen en standaard salaris schalen van CAO UMCs 2013-2015.

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Tabel 3: Berekening eenheidsprijs tandarts.

Berekening eenheidsprijs (minuut) tandarts

Norminkomen tandarts* € 110.881 Overige praktijkkosten (incl. personeel en materiaal)*

€ 129.151

Aantal werkzame uren per jaar** 1907 Aantal patiënt gebonden uren per jaar** 1449,26 Uurtarief tandarts per patiënt gebonden uur € 165,62 Eenheidstarief tandarts (minuut) € 2,76 * www.nza.nl ** bepaald op basis van feiten en cijfers tandheelkunde NMT 2011. Waarin aangegeven staat dat de gemiddelde tandarts een werkweek heeft van 39,9 uur en hiervan 31,1 uur aan de stoel werkt. Uitgegaan van 21 vakantie dagen en gemiddeld 6 feestdagen per jaar. Tabel 4: Berekening eenheidsprijs kaakchirurg.

Berekening eenheidsprijs (minuut) kaakchirurg

Bruto loon per jaar volgens CAO* € 118.812 Toeslag 35% voor overige kosten zoals sociale premies en vakantiegeld*

€ 41.584

Toeslag functie gebonden kosten volgens CAO UMC’s**

€ 4.988

Totaal per jaar € 165.384 Aantal werkzame uren per jaar* 2100 Aantal patiënt gebonden uren per jaar (70%)* 1470 Uurtarief kaakchirurg per patiënt gebonden uur € 112,51 Eenheidstarief kaakchirurg (minuut) € 1,88 * Handleiding kostenonderzoek Hakkaart-van Royen. ** CAO UMC’s 2013-2015. Aan de hand van handleiding kostenonderzoek Hakkaart-van Royen trap 4 van salarisschaal, maandbedrag o.b.v. volledige arbeidsduur € 9.901 Tabel 5: Berekening eenheidstarief ondersteunend personeel kaakchirurg.

Berekening eenheidsprijs (minuut) ondersteunend personeel kaakchirurg

Bruto loon per jaar volgens CAO** € 35.688 Toeslag 39% voor overige kosten zoals sociale premies en vakantiegeld*

€ 13.918,32

Totaal per jaar € 49.606,32 Aantal werkzame uren per jaar* 1540 Uurtarief ondersteunend personeel per patiënt gebonden uur

€ 32,21

Eenheidstarief ondersteunend personeel € 0,54 * Handleiding kostenonderzoek Hakkaart-van Royen. ** CAO UMC’s 2013-2015. Volgens handleiding kostenonderzoek Hakkaart-van Royen salarisschaal 8, trap 6. Maandbedrag o.b.v. volledige arbeidsduur € 2.974

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Annex 2: uitkomstmaten Voor het meten van de effecten is gebruik gemaakt van de volgende 3 uitkomstmaten:

• SF36 is een, oorspronkelijk Engelstalige, betrouwbare en valide gezondheidsvragenlijst om de fysieke en psychische gezondheid die door een patiënt ervaren wordt te meten. 25 Deze vragenlijst bestaat uit 36 vragen en gestandaardiseerde antwoord keuzes welke zijn georganiseerd in acht multi-punt schalen. Alle scores worden vervolgens omgezet naar een 0-100 schaal, waarbij een hoge score een hoger niveau van welzijn aangeeft. Met behulp van een SF-6D excel logaritme van de Universiteit van Sheffield zijn deze SF36 scores vervolgens omgezet in QALY’s, waarbij is aangenomen dat het de gemeten kwaliteit van leven een jaar aanhoud. QALY staat voor Quality-Adjusted Life Year, dit is een maat voor gezondheid waarbij de levensverwachting wordt gecorrigeerd met een kwaliteitsfactor (ook wel ‘utiliteit’ genoemd). Utiliteit is een begrip dat staat voor de waarde die een individu toekent aan de consequenties van verschillende handelingsalternatieven in een situatie van onzekerheid. Het principe is dat alle gezondheidswinst uitgedrukt kan worden in ofwel een verbeterde levensverwachting ofwel een verbeterde (gezondheid gerelateerde) kwaliteit van leven. Via een zogenoemde utiliteitsmeting worden kwaliteitsgewichten bepaald, die aan levensjaren in een bepaalde toestand kunnen worden gekoppeld. 18 Wisløff et al. beschreven dat de toe- of afname van de QALY door medische technologie over het algemeen klein is (met de kanttekening dat de variatie onderling groot is) en dat er een versterking van de toename waarneembaar is wanneer de tijdshorizon van de studie toeneemt. Ter illustratie in slechts 30% van de door hen beoordeelde studies was er een toename van 0.25 QALY of meer gerapporteerd. In het geval van kankerbehandeling werd een toename van QALY’s gevonden met een mediaan van 0.07 met een interkwartielafstand van 0.31.31

• Mondgezondheid in relatie tot kwaliteit van leven wordt gemeten door middel van een vragenlijst, de OHIP–NL49. Dit is de Nederlandse vertaling van de Oral Health Impact Profile (OHIP) vragenlijst van de World Health Organization (WHO). Deze betrouwbare en gevalideerde vragenlijst meet de impact van de gebitssituatie op de levenskwaliteit. 21,22 De vragenlijst bestaat uit 49 vragen met een 5 puntenschaal. Hierdoor komt er een score uit van 0-196 punten. Een lage score geeft een hoge mondgezondheid gerelateerde kwaliteit van leven weer. Het interpreteren van een toe- of afname van zo een OHIP punt is lastig. Er zijn een aantal studies die hou vast bieden. John et al. bepaalden een ‘minimal importance difference’ of MID voor het gebruik van de OHIP maat in de prothetische tandheelkunde. MID definieerden zij als: “het kleinste verschil in score op het gebied van belang dat patiënten ervaren als nuttig, welke mandaat zou moeten geven, bij het ontbreken van vervelende bijwerkingen en hoge kosten, voor een verandering in de behandelstrategie van de patiënt.” De MID stelden zij vast op 6 OHIP punten (95% betrouwbaarheidsinterval: 2 tot 9). 35

• Mixing index (MI). Dit is een valide en betrouwbare methode om het kauwvermogen van de patiënt te beoordelen. De MI meet dit met behulp van een wassen kauwblokje, bestaande uit een rode en blauwe waslaag. De patiënt wordt gevraagd op dit blokje te kauwen (20 kauwslagen). Dit blokje wordt hierna met behulp van een hydraulische handpers (50 bar) tot een dikte van 2 mm plat gemaakt. Vervolgens wordt een digitale opname gemaakt van het blokje met een hoogwaardige scanner. De verspreiding van de kleurintensiteit van de beide kleuren en het ontstaan van tussenliggende kleuren geven de mate van kauwfunctie weer. Vervolgens is de mixing index bepaald. Een lagere score geeft een betere kauwfunctie weer. 23,24 Ter bevordering van het begrip met betrekking tot de uitkomstmaat kan een vergelijking met het gebruik van de uitkomstmaat in de orale oncologie illustratief zijn. Onderzoek laat zien dat het kauwvermogen van patiënten met een plaveiselcelcarcinoom van de tong en / of mondbodem kort na chirurgie af nam door een toename van de MI score met 4 punten (p = .001). Een half jaar na chirurgie herstelde hij enigszins, waardoor de MI score netto met 2 punten (p = .045) steeg en het kauwvermogen dus af is genomen. Bij de baseline (voor

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chirurgie) was het kauwvermogen gelijk aan dat van gezonde personen met een volledige prothese, na chirurgie was het kauwvermogen significant slechter dan de gezonde controle groep met natuurlijke dentitie (p =.000) en slechter dan de gezonde controle groep met een volledige prothese ( p <.05). 36 Hierbij moet in het achterhoofd gehouden worden dat statistische significantie niet noodzakelijkerwijs klinische relevantie weergeeft.

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Annex 3: Originele data uitkomstmaten In tabel 6 is een overzicht gegeven van de originele data van de uitkomstmaten met de daarbij horende gemiddelden. Tabel 6: Originele data uitkomstmaten voor Removable Partial Dentures (RPD) en Implant Supported Removable Partial Dentures (ISRPD). Gebruikte uitkomstmaten zijn de SF36, Oral Health Impact Profile (OHIP), Mixing Index (MI) en de Quality Adjusted Life Years (QALY).

RPD ISRPD Patient SF36 OHIP MI QALY SF36 OHIP MI QALY 1 652 23 18,1 0,7192 717 13 17,9 0,7779 2 798 19 22,3 0,9099 781 5 17,8 0,9164 3 798 37 18,2 0,7685 739 11 18,7 0,8083 4 815 20 19,9 0,8021 648 5 17,6 0,7542 5 748 4 19,3 0,7685 598 2 19,7 0,6757 6 511 45 22 0,6042 431 45 20,4 0,5672 7 807 5 18,9 0,8272 794 3 17,3 0,8543 8 827 25 19,6 0,9099 840 10 17,3 0,9164 9 830 28 21 0,9435 765 11 18,6 0,8313 10 610 39 19,3 0,7683 725 30 18 0,8272 11 831 26 18,7 0,8828 830 10 18,2 0,9164 Gemiddelde 748 25 20 0,8095 715 13 18 0,8041

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