Multifactorial Risk Assessment for Survival Of

JJOD-2117; No. of Pages 6

Multifactorial risk assessment for survival ofabutments of removable partial dentures based onpractice-based longitudinal study

Sayaka Tada, Kazunori Ikebe *, Ken-ichi Matsuda, Yoshinobu Maeda

Department of Prosthodontics, Gerodontology and Oral Rehabilitation, Osaka University Graduate School of Dentistry,

Japan

j o u r n a l o f d e n t i s t r y x x x ( 2 0 1 3 ) x x x – x x x

a r t i c l e i n f o

Article history:

Received 25 May 2013

Received in revised form

18 July 2013

Accepted 23 July 2013

Available online xxx

Keywords:

Abutment

Removable partial denture

Survival rate

Multifactorial risk assessment

Longitudinal study

a b s t r a c t

Objectives: Predicting the tooth survival is such a great challenge for evidence-based den-

tistry. To prevent further tooth loss of partially edentulous patients, estimation of individ-

ualized risk and benefit for each residual tooth is important to the clinical decision-making.

While there are several reports indicating a risk of losing the abutment teeth of RPDs, there

are no existing reports exploring the cause of abutment loss by multifactorial analysis. The

aim of this practice-based longitudinal study was to determine the prognostic factors

affecting the survival period of RPD abutments using a multifactorial risk assessment.

Methods: One hundred and forty-seven patients had been previously provided with a total of

236 new RPDs at the Osaka University Dental Hospital; the 856 abutments for these RPDs

were analyzed. Survival of abutment teeth was estimated using the Kaplan–Meier method.

Multivariate analysis was conducted by Cox’s proportional hazard modelling.

Results: The 5-year survival rates were 86.6% for direct abutments and 93.1% for indirect

abutments, compared with 95.8% survival in non-abutment teeth. The multivariate analysis

showed that abutment survival was significantly associated with crown-root ratio (hazard

ratio (HR): 3.13), root canal treatment (HR: 2.93), pocket depth (HR: 2.51), type of abutments

(HR: 2.19) and occlusal support (HR: 1.90).

Conclusion: From this practice-based longitudinal study, we concluded that RPD abutment

teeth are more likely to be lost than other residual teeth. From the multifactorial risk factor

assessment, several prognostic factors, such as occlusal support, crown-root ratio, root

canal treatment, and pocket depth were suggested.

Clinical significance: These results could be used to estimate the individualized risk for the

residual teeth, to predict the prognosis of RPD abutments and to facilitate an evidence-based

clinical decision making.

# 2013 Elsevier Ltd. All rights reserved.

Available online at www.sciencedirect.com

journal homepage: www.intl.elsevierhealth.com/journals/jden

1. Introduction

When designing and providing dental prosthesis, it is very

important to estimate the individualized risk and benefit of

* Corresponding author at: Department of Prosthodontics, GerodontolDentistry, 1-8 Yamadaoka Suita, Osaka 565-0871, Japan. Tel.: +81 6 68

E-mail address: [email protected] (K. Ikebe).

Please cite this article in press as: Tada S, et al. Multifactorial risk assessmpractice-based longitudinal study. Journal of Dentistry (2013), http://dx.d

0300-5712/$ – see front matter # 2013 Elsevier Ltd. All rights reservedhttp://dx.doi.org/10.1016/j.jdent.2013.07.018

the prosthesis for the residual teeth. In planning dental

treatment for patients with tooth loss, the potential impact of

replacement prostheses on dental health must be considered

carefully. The concept of ‘‘biological price’’1 is frequently

described, and the replacement of missing teeth should be

ogy and Oral Rehabilitation, Osaka University Graduate School of79 2956; fax: +81 6 6879 2957.

ent for survival of abutments of removable partial dentures based onoi.org/10.1016/j.jdent.2013.07.018

.

http://dx.doi.org/10.1016/j.jdent.2013.07.018

mailto:[email protected]


http://www.sciencedirect.com/science/journal/03005712


j o u r n a l o f d e n t i s t r y x x x ( 2 0 1 3 ) x x x – x x x2


balanced with the potential for a prosthesis to contribute to

dental and periodontal diseases. This is particularly relevant

to the teeth used as abutments for fixed and removable partial

dentures (RPDs).

Various reports have referred to the association between

replacement prostheses, particularly RPDs, and dental dis-

eases.2 The abutment teeth of RPDs were reported to be at

higher risk of periodontitis,3,4 dental caries5,6 and root

fracture7 than other teeth. Longitudinal studies have also

shown that RPD abutments were at the increased risk of

loss.8,9

Tooth loss, especially in the case of abutment teeth, is

intrinsically involved in complex relationship with many

factors in the long term. However, while this mandates a

multifactorial analysis using practice-based research to exam-

ine the significant risk factors determining tooth loss, such

analysis has not been reported yet for RPD abutment teeth.

As long as RPDs remain a common treatment option for

partially edentulous patients, it is imperative to know the

specific prognostic factors dictating the survival of RPD

abutments, and their relative contribution to the duration of

tooth survival. This knowledge facilitates the development of

prosthodontic treatment strategy and the evidence-based

prediction of long-term prognosis for those abutment teeth.

The absence of any such risk assessment denies us a practical

way for predicting the survival period of each abutment

depending on their individual characteristics.

This longitudinal retrospective cohort study aimed to fill

this void by examining the survival of RPD abutments in

longitudinal clinical cases, and exploring the prognostic

factors dictating survival and their relative contribution to

tooth loss.

2. Methods

2.1. Study population

We targeted all patients provided with RPDs between January

2002 and December 2003 in Removable Prosthodontics

department of Osaka University Dental Hospital, Japan. The

protocol of this study was approved by the School of Dentistry

Ethics Committee (No. H22-E2). Patients were included if they

had been provided with a clasp-retained, cobalt–chromium-

designed and tooth-supported RPD which is covered by

Japanese medical insurance and had used it for 2 years or

more, and were excluded if their dentures were immediate

RPDs that required fixing, and dentures with complex designs

such as maxillofacial prostheses, attachment-retained or

lingual-plate-connected dentures. In addition, we excluded

patients who had not received conservative periodontal

intervention or maintenance at least once a year during the

observation period.

RPDs were provided by prosthodontists certificated by

Japan Prosthodontic Society. Periodontal maintenance was

performed by dentists in the preventive or periodontal

departments. Data were gathered from the dental records,

and patients were examined by the attending prosthodontists

at the time of RPD provision. These data included general and

oral status, and RPD’s design.


2.2. Variables

Variables set as patient-related factors were: gender (male/

female), age (<65 or �65 years), lifestyle-related disease

(with: having a medical history of at least one of hyperten-

sion, diabetes mellitus or dyslipidemia/without: having no

medical history of these diseases) and occlusal support

(A + B1/B2/B3/B4/C, based on the Eichner classification10,11).

Tooth-related factors were: jaw (upper/lower), type of tooth

(incisor/canine/premolar/molar), existing root canal treat-

ment (with/without), pocket depth (PD: �3 mm/4 mm/

5 mm/�6 mm), crown-root ratio (<1.0/1.0–1.5/�1.5) and type

of abutment (direct: abutment in contact with direct

retainer/indirect: abutment in contact with indirect retain-

er). Root canal treatment and crown-root ratio were

determined from the radiographs taken at the time of prosthetic

diagnosis.

2.3. Statistical analysis

Kaplan–Meier survival analysis12 was performed to show the

survival curve of direct and indirect abutments, as well as the

other residual teeth. The survival distribution was then

compared with a log-rank test. p-values less than 0.05 were

considered to be statistically significant. The Bonferroni

correction methods for counteracting the problem of multiple

comparisons were used.

Cox’s proportional hazard analysis was used to test

bivariate and multivariate associations between each variable

and the abutment survival time. For the multivariate model,

variables for which the bivariable p-value less than 0.25 were

considered as prognostic variables by the stepwise backward

selection (adoption criterion: p < 0.05, exception criterion:

p < 0.10). Cases where data for the prognostic variables were

missing were deleted.

We defined the entry-point as the date of provision

of RPDs and the end-point as either the date of the last

visit to the hospital, which was treated as a censoring, or

the date of abutment tooth loss (defined as extraction of the

tooth or changes to metal or resin coping of the over

denture).

Data were analyzed using PASW Statistics 18 software

(formerly SPSS; IBM Company, Tokyo, Japan).

3. Results

3.1. Demographics

One hundred and forty-seven patients satisfied the inclusion

criteria and had been provided with a total of 236 RPDs. The

total numbers of RPD abutments were 856 and the study

sample contained a further 1114 residual (non-abutment)

teeth (Table 1).

3.2. Clinical outcomes

During the observation period, 13.7% of the abutments were

lost (in contrast to 4.4% of non-abutment teeth), including

17.9% of direct and 8.5% of indirect abutments.



Table 1 – Characteristics of patients and removablepartial dentures.

Patients Total number 147

Gender (male/female) 55 (37%)/92 (63%)

Age (year) 64.2 � 8.7 (SD)

Occlusal support

(Eichner classification)

A = 13, B1 = 27,

B2 = 34, B3 = 32,

B4 = 28, C = 13

Dentures Total number 236

Upper/lower 113 (48%)/123 (52%)

Mean usage period 5 year 5 months

(64.8 � 16.9 (SD) months)

Mean number of

artificial teeth/a RPD

5.3 � 2.7 (SD)

Mean number of

abutment teeth/a RPD

3.7 � 1.1 (SD)

Abutments Total number 856

Type (direct/indirect) 469 (55%)/387 (45%)

SD, standard deviation; RPD, removable partial denture.

Fig. 1 – Kaplan–Meier survival curves for non-abutment,

indirect abutment and direct abutment teeth.

j o u r n a l o f d e n t i s t r y x x x ( 2 0 1 3 ) x x x – x x x 3


3.3. Survival curves

The Kaplan–Meier survival curve is shown in Fig. 1. The 5-year

survival rate was 95.8% for non-abutment teeth, 93.1% for

indirect abutments and 86.6% for direct abutments. In the log-

rank test, significant differences between these three groups

were observed by multiple comparison tests.

3.4. Bivariate analysis

Bivariate analysis by using Cox’s proportional hazard

modelling indicated that significant variables were occlusal

support, root canal treatment, pocket depth, crown-root ratio

and type of abutment (Table 2). In the case of occlusal support,

because the statistical difference between A-B2 and B3-C was

apparent, we divided subjects into two groups and re-

analyzed. For the same reason, in the section of pocket depth

and crown-root ratio, subjects were also divided into two

groups, respectively. Results for these analyses are also

shown in Table 2.

3.5. Multivariate analysis

Variables selection for the multivariate model was performed

by the backward selection technique. The final Cox’s propor-

tional hazard model indicated that crown-root ratio (hazard

ratio (HR): 3.13), root canal treatment (HR: 2.93), pocket depth

(HR: 2.51), type of abutments (HR: 2.19) and occlusal support

(HR: 1.90), and were significant prognostic factors in the

abutment survival period (Table 3).

4. Discussion

This longitudinal prospective cohort study indicates the

expected survival trends of RPD abutments, identifies several

significant prognostic factors related to their survival and

generates numeric hazard ratio (HR) values to quantitatively

estimate the extent to which these factors influence their

survival. These novel findings can help us to predict the


survival prospects for abutment teeth at the time of diagnosis

based on their individual characteristics.

The result of the Kaplan–Meier analysis showed that the

survival rate of abutment teeth was significantly lower than

that of non-abutment teeth. A recent clinical study, following

100 patients after periodontal therapy over 10 years, showed

that 18% of RPD abutment teeth were lost, compared with only

6% of non-abutment teeth.13 Other previous research has

suggested that being an abutment of RPDs was a significant

risk factor for tooth loss.8,9,13,14 This is likely due to the

continuous and repetitive mechanical stress with which these

teeth are loaded, the attendant higher risk of damage to the

periodontal tissue. It was also reported that the presence of

RPD retainers can contribute to deterioration in dental hygiene

around abutment teeth.6,15–18

However, survival curves of RPD abutments based on large

number of longitudinal clinical cases have not previously been

reported. Much of the published clinical research19–22 evalu-

ated only the frequency with which abutment teeth are lost,

but this type of censored data do not provide a good prognostic

indication of tooth survival. The Kaplan–Meier method and

Cox’s proportional hazard regression analysis used in this

study are representative ways of performing survival analysis

using the censoring.23

In the multivariate analysis of our data by using Cox’s

proportional hazard regression model, we collected the

objective information about potential factors (both patient-

related and tooth-related), which can be evaluated easily and

correctly by any dentist. This multivariate regression analysis

indicated several independently significant prognostic factors.

Occlusal support area was one of the significant prognostic

factors. In a 28-year follow-up survey, it was indicated that the



Table 2 – Bivariate analysis for prognostic factors affecting survival of RPD abutments using the Cox’s proportional hazardmodel.

Variable Reference Number of teeth Loss of teeth HR 95% CI p-Value

Gender Male 359 46 1

Female 497 71 1.06 0.73–1.53 0.775

Age Under 65 393 55 1

65 or more 497 62 0.98 0.68–1.41 0.910

Lifestyle-related Diseases Without 521 64 1

With 335 53 0.30 0.91–1.88 0.154*

Occlusal support A and B1 203 16 1

B2 199 17 0.90 0.45–1.78 0.759

B3 219 42 2.33 1.31–4.15 0.004*

B4 156 28 2.04 1.10–3.77 0.023*

C 79 14 2.18 1.06–4.47 0.033*

A-B2 402 33 1

B3-C 454 84 2.33 1.56–3.48 <0.001*

Upper/lower Lower 454 61 1

Upper 402 56 1.06 0.74–1.52 0.761

Type of teeth Canine 212 27 1

Premolar 462 56 0.94 0.60–1.49 0.806

Molar 161 28 1.48 0.87–2.50 0.149*

Incisor 21 6 2.85 1.17–6.90 0.021*

Type of abutment Indirect 387 33 1

Direct 469 84 2.16 1.44–3.23 <0.001*

Root canal treatment Without 462 38 1

With 394 79 2.52 1.71–3.72 <0.001*

Pocket depth 3 mm or less 510 48 1

4 mm 130 13 1 0.58–1.99 0.814

5 mm 56 15 3.04 1.70–5.42 <0.001*

6 mm or more 76 25 4.14 2.55–6.71 <0.001*

4 mm or less 640 61 1

5 mm or more 132 40 3.59 2.41–5.34 <0.001*

Crown-root ratio Less than1.0 486 48 1

1.0–1.5 195 20 1.09 0.65–1.83 0.756

More than 1.5 105 39 4.64 3.04–7.08 <0.001*

Less than 1.5 681 68 1

1.5 or more 105 39 4.53 3.05–6.72 <0.001*

HR, hazard ratio; CI, confidence interval.

Occlusal support was classified based on the Eichner classification.* Variables with p < 0.25 were considered as potential prognostic factors.



number of residual teeth at baseline significantly influenced

tooth loss, with fewer residual teeth tending to increase tooth

loss.24 In another report, patients using free-end-saddle-type

RPDs tended to experience more abutment loss. Moreover,

the survival period of abutments was shorter for bilateral

free-end-saddle-type RPDs than for unilateral ones.20 Both

results may indicate that a decrease in the number of residual

teeth, and therefore in the occlusal support area, has the

potential to cause occlusal instability, increasing the occlusal

load on the abutment teeth, and damaging the underlying

periodontal tissue. In addition, our findings suggest that the

presence of bilateral premolar occlusal support may be

crucial for the stability of the occlusal position, as indicated


by the large statistical difference between the A-B2 and B3-C

groups.

Both the crown-root ratio and pocket depth (PD) were

prognostic factors affecting the survival period. The estima-

tion of crown-root ratio is achieved simply through objective

measurement of a radiographic image. In general, we consider

the crown-root ratio an important criterion in selecting

suitable abutment teeth for RPDs.25 Teeth are adjudged to

be unsuitable as abutments if there is alveolar bone resorption

of over half of the total root length. However, from the result of

this bivariate analysis, there was little difference between

the ‘‘<1.0’’ and ‘‘1.0–1.5’’ groups (HR: 1.08, p = 0.756). So far,

there were quite few reports about the relationship between



Table 3 – Multivariate analysis for prognostic factorsaffecting survival of RPDs abutments using Cox’s pro-portional hazard model.

Variable Reference HR 95% CI p-Value

Crown-root

ratio

Under 1.5 1

Over 1.5 3.13 2.00–4.90 <0.001

Root canal

treatment

Without 1

With 2.93 1.85–4.63 <0.001

Pocket depth 4 mm or less 1

5 mm or more 2.51 1.61–3.91 <0.001

Type of

abutment

Indirect 1

Direct 2.19 1.36–3.52 0.001

Occlusal

support

A-B2 1

B3-C 1.90 1.17–3.10 0.010

HR, hazard ratio; CI, confidence interval.

Occlusal support was classified based on the Eichner classification.

Variables with p < 0.25 in the bivariate analysis were considered as

prognostic variables by stepwise backward selection (adoption

criterion: p < 0.05, exception criterion: p < 0.10).

j o u r n a l o f d e n t i s t r y x x x ( 2 0 1 3 ) x x x – x x x 5


crown-root ratio and the tooth survival time.26 PD is another

reliable objective index for evaluating periodontal condition.

Matuliene et al. reported that, from multivariate analysis of

the association between PD and tooth loss, PD of 5 mm and

over represented a significant risk factor, compared with PD of

3 mm or less.27 The corresponding odds ratios in that study for

PD = 4, 5, 6 and 7 mm and more were 1.6 ( p = 0.034), 3.0

( p < 0.0001), 2.7 ( p = 0.005) and 9.9 ( p < 0.0001), respectively.

Consistent with this previous work, we showed that abut-

ments with 5 mm PD and more were statistically at higher risk

of teeth loss. Our bivariate analysis showed that the HR of

4 mm PD compared with 3 mm PD was 1.00 ( p = 0.814),

suggesting no difference in the risk of tooth loss.

The existence of previous root canal treatment also

independently affected the survival time of abutment teeth.

So far it has been reported that the 4-year survival rate of 759

teeth following primary root canal treatment were 95%.28

Conversely, in case of the 410 abutment teeth of RPD after root

canal treatment, the 5-year survival rate was only 51%.29 This

difference suggests that a retainer for RPD might deteriorate

survival of endodontically treated teeth, rather than existence

of root canal treatment itself. The mechanical stress from the

RPD must increase the risk of that tooth fracturing.

There was a significant difference of the survival rates

between direct and indirect abutment teeth, indicating that the

type of abutments was also a prognostic factor. No existing

reports have compared direct and indirect RPD abutment teeth.

RPD abutments continuously loaded the mechanical and

bacterial stress from RPDs and have a higher risk to damage the

periodontal tissue than non-abutment teeth. Especially, direct

abutment teeth experience continuous and repetitive mechan-

ical loading (including the rotational and settling movements of

the RPD) much more directly than indirect abutment teeth.

This study also calculated the HR of each factor. For

instance, the HR of the type of abutment showed that indirect

abutments were likely to survive 2.19 times longer than direct

abutments after controlling for other factors. Importantly, by

using Cox’s hazard regression model, we can also calculate the

individual survival probability of the abutment teeth at any


given point in time under each specific condition, giving us

previously unprecedented prognostic power.

As the patients in this study were limited to those attending

a university hospital, and might therefore be a selective

sample, it is possible that other prognostic factors could arise

in other trials, or that the quantitative differences determined

here might change. However, we included all the patients

satisfying appropriate selection criteria over a 2-year period:

this type of continuous sampling minimizes any selection bias.

All RPDs were provided by a limited number of operators with

advanced training in prosthodontics, after preparation of the

mouth for RPD treatment by suitably qualified dental profes-

sionals. The patients visited the hospital regularly for peri-

odontal maintenance, including scaling, root planning and

tooth polishing, throughout the observation period. Therefore,

we are confident that the significant prognostic factors found in

this research are an accurate reflection of those affecting the

survival of RPD abutments in general population.

5. Conclusion

We conclude that RPD abutment teeth are more likely to be

lost than other residual teeth. Occlusal support, crown-root

ratio, root canal treatment, pocket depth and type of abutment

are related to the survival time of RPD abutments. These

results will help us to estimate the individualized risk and

benefit of the prosthodontic treatment for the residual teeth,

to evaluate the prognosis of RPD abutments and also to

develop evidence-based dentistry in practice.

Conflict of interest

There is no conflict of interest.

Acknowledgments

We would like to express our deepest gratitude to Professor

Finbarr P. Allen, for providing carefully considered feedback

and valuable comments. We are also indebted to Professor

Hirofumi Yatani for his invaluable comments and warm

encouragements. This research was supported by a Grant-in-

Aid for Scientific Research (No. 22592149) from the Japan

Society for the Promotion of Science.

r e f e r e n c e s

1. Zarb GA, MacKay HF. The partially edentulous patient, I. Thebiologic price of prosthodontic intervention. AustralianDental Journal 1980;25:63–8.

2. Preshaw PM, Walls AWG, Jakubovics NS, Moynihan PJ,Jepson NJA, Loewy Z. Association of removable partialdenture use with oral and systemic health. Journal ofDentistry 2011;39:711–9.

3. Zlataric DK, Celebic A, Valentic-Peruzonic M. The effect ofremovable partial dentures on periodontal health ofabutment and non-abutment teeth. Journal of Periodontology2002;73:137–44.


http://refhub.elsevier.com/S0300-5712(13)00191-7/sbref0005














4. Sato F, Koyama S, Chiba T, Kadowaki K, Kawata T, Sasaki K.Changes in periodontal conditions of remaining teeth fiveyears after RPD placement. Annals of Japan ProsthodonticSociety 2009;1:130–8. [in Japanese].

5. Bergman B, Hugoson A, Olsson CO. Caries, periodontal andprosthetic findings in patients with removable partialdentures: a ten-year longitudinal study. Journal of ProstheticDentistry 1982;48:506–14.

6. Jepson NJA, Moynihan PJ, Kelly PJ, Waston GW, ThomasonJM. Caries incidence following restoration of shortenedlower dental arches in a randomized controlled trial. BritishDental Journal 2001;191:140–4.

7. Matsuda K, Ikebe K, Enoki K, Tada S, Fujiwara K, Maeda Y.Incidence and association of root fractures after prosthetictreatment. Journal of Prosthodontic Research 2011;55:137–40.

8. Miyamoto T, Morgano SM, Kumagai T, Jones JA, Nunn ME.Treatment history of teeth in relation to the longevity of theteeth and their restorations: outcomes of teeth treated andmaintained for 15 years. Journal of Prosthetic Dentistry2007;97:150–6.

9. Nevalainen MJ, Narhi TO, Ainamo A. A 5-year follow-upstudy on the prosthetic rehabilitation of the elderly inHelsinki, Finland. Journal of Oral Rehabilitation 2004;31:647–52.[in Japanese].

10. Eichner K. Renewed examination of the group classificationof partially edentulous arches by Eichner and applicationadvices for studies on morbidity statistics. Stomatologie derDDR 1990;40:321–5.

11. Ikebe K, Matsuda K, Kagawa R, Enoki K, Okada T, Yoshida M,et al. Masticatory performance in older subjects with varyingdegrees of tooth loss. Journal of Dentistry 2012;40:71–6.

12. Opdam NJM, Bronkhorst EM, Cenci MS, Huysmans MCDNJM,Wilson NHF. Age of failed restorations: a deceptive longevityparameter. Journal of Dentistry 2011;39:225–30.

13. Pretzl B, Kaltschmitt J, Kim TS, Reitmeir P, Eickholz P. Toothloss after active periodontal therapy. 2: Tooth-relatedfactors. Journal of Clinical Periodontology 2008;35:175–82.

14. Hirotomi T, Yoshihara A, Ogawa H, Miyazaki H. Tooth-relatedrisk factors for tooth loss in community-dwelling elderlypeople. Community Dentistry and Oral Epidemiology 2012;40:154–63.

15. Steel JG, Walls AWG, Murray JJ. Partial dentures as anindependent indicator of root caries risk in a group of olderadults. Gerodontology 1998;14:67–74.


16. Steel JG, Sheiham A, Marcenes W, Fay N, Walls AWG.Clinical and behavior risk indicators for root caries in olderpeople. Gerodontology 2001;18:95–101.

17. Drake CW, Beck JD. The oral status of elderly removablepartial denture wears. Journal of Oral Rehabilitation1993;20:53–60.

18. Tanaka J, Tanaka M, Kawazoe T. Longitudinal research onthe oral environment of elderly wearing fixed or removableprostheses. Journal of Prosthodontic Research 2009;53:83–8.

19. Kern M, Wagner B. Periodontal findings in patients 10 yearsafter insertion of removable partial dentures. Journal of OralRehabilitation 2001;28:991–7.

20. Vanzeveren C, D’hoore W, Bercy P, Leloup G. Treatmentwith removable partial dentures: a longitudinal study. PartII. Journal of Oral Rehabilitation 2003;30:459–69.

21. Saito M, Kotani K, Miura Y, Kawasaki T. Complication andfailures in removable partial dentures: a clinical evaluation.Journal of Oral Rehabilitation 2002;29:627–33.

22. Piwowarczyk A, Kohler KC, Bender R, Buchler A, Lauer HC,Ottl P. Prognosis for abutment teeth of removable dentures:a retrospective study. Journal of Prosthodontics 2007;16:377–82.

23. Hannigan A, Lynch CD. Statistical methodology in oral anddental research: pitfalls and recommendations. Journal ofDentistry 2013;41:385–92.

24. Burt BA, Ismail AI, Morrison EC, Eltran ED. Risk factors fortooth loss over a 28-year period. Journal of Dental Research1990;69:1126–30.

25. Carr AB, McGivney GP, Brown DT. McCracken’s removablepartial prosthodontics. 11th ed. St. Louis: Elsevier; 2004:189–229.

26. Grossmann Y, Sadan A. The prosthodontic concept ofcrown-to-root ratio: a review of the literature. Journal ofProsthetic Dentistry 2005;93:559–62.

27. Matuliene G, Pjetursson BE, Salvi GE, Schmidlin K, Bragger U,Zwahlen M, et al. Influence of residual pockets on progressionof periodontitis and tooth loss: results after 11 years ofmaintenance. Journal of Clinical Periodontology 2008;35:685–95.

28. Ng YL, Mann V, Gulabivala K. A prospective study of thefactors affecting outcomes of non-surgical root canaltreatment: Part 2: Tooth survival. International EndodonticJournal 2011;44:610–25.

29. Wegner PK, Freitag S, Kern M. Survival rate ofendodontically treated teeth with posts after prostheticrestoration. Journal of Endodontics 2006;32:928–31.






























































































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Multifactorial Risk Assessment for Survival Of