long-term retrospective study of narrow implants; 1-12 ... · cumulative survival rate and success...

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Long-term retrospective study of narrow implants; 1-12 years of

cumulative success rate

Hyun-Min Kim

Department of Dental Science

The Graduate School, Yonsei University

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Long-term retrospective study of

narrow implants; 1-12 years of cumulative success rate

비교

Directed by Professor Jung-Kiu Chai

The Master's Thesis submitted to the Department of Dental Science,

the Graduate School of Yonsei University in partial fulfillment of the requirements for the degree of

Master of Dental Science

Hyun-Min Kim

June 2011

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This certifies that the Master’s Thesis of Hyun-Min Kim is approved

___________________________________________________________________

Thesis Supervisor : Jung-Kiu Chai

Seong-Ho Choi

Ui-Won Jung

The Graduate School Yonsei University

June 2011

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TABLE OF CONTENTS

ABSTRACT (ENGLISH) ························································································· iv

I. INTRODUCTION ···································································································1

II. MATERIALS AND METHODS ·······································································4

III. RESULTS ················································································································7

IV. DISCUSSION ········································································································10

V. CONCLUSION ·····································································································13

REFERENCES ··········································································································14

TABLES ·························································································································19

FIGURES ·················································································································22

ABSTRACT (KOREAN) ························································································25

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LIST OF TABLES

Table 1. Distribution of implants according to patients’ age and

gender························································································19

Table 2. Distribution of implants according to diameter and length ····································································································19

Table 3. Distribution of bone quality····················································20

Table 4. Distribution of prosthesis type·······························20

Table 5. Comparisons of the survival rates and p-values. ··············20

Table 6. Types and Numbers of complications··································21

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LIST OF FIGURES

Figure 1. Kaplan-Meier survival curve of the implants····················22

Figure 2. Kaplan-Meier success curve of the implants ···················22

Figure 3. Kaplan-Meier success curves for implants according to

patient’s age····································································23


bone quality····································································23


implant systems·····································································24

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ABSTRACT



Hyun-Min Kim, D.D.S.



(Directed by Prof. Jung-Kiu Chai, D.D.S., M.S.D., PhD.)

The selection of implant diameter depends on the type of edentulism, the amount of

the residual bone, the volume of space available for the prosthetic rehabilitation, the

emergence profile, and the type of occlusion. Narrow-diameter implants (NIs) were

designed specifically for decreased interradicular bone, a thin alveolar crest and the

replacement of teeth with small cervical diameters, like mandibular incisors and

maxillary lateral teeth. The objective of this study was to evaluate long term survival

and success rates of the NIs placed with various implant system, and analyze the

associated biological and mechanical complications.

A total of 338 patients (male = 45.6%, female = 54.4%) who received 541 NIs (≤

3.5 mm in diameter) were enrolled in this study. Life table analysis with the

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cumulative survival rate and success rate was calculated. The results are as follows:

Six implants were lost in the maxilla, while 3 implants were lost in the mandible. The

cumulative survival rates of NIs were 98.1% and 98.5% for the implant- and subject-

based analysis, respectively. The cumulative success rates were 91.8% and 93.8% for

the implant- and subject-based analysis, respectively. The infection was the highest

reason of the biological complication. The most frequent mechanical complication

was the decementation. The mechanical complications were more frequent than the

biological complications.

In conclusion, the use of NIs could be suggested in the narrow alveolar ridge or

narrow mesiodistal space, on the basis of the high survival rate with less complication

in this study.

_____________________________________________________________________

Key words: narrow-diameter implants; the cumulative survival rate and success rate;

complication

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Hyun-Min Kim, D.D.S.



(Directed by Prof. Jung-Kiu Chai, D.D.S., M.S.D., PhD.)

I. INTRODUCTION

The selection of implant diameter depends on the type of edentulism, the amount

of the residual bone, the volume of space available for the prosthetic rehabilitation,

the emergence profile, and the type of occlusion1. Although many implant systems

having various diameter have been developed, the diameter of 3.75 to 4.0 mm is still

referred to as a ‘standard’ of implant. An implant having smaller diameter has been

categorized into a ‘narrow’ one.

In the early period of implant dentistry, ‘longer and wider’ implants had been

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preferred at the clinical and research fields2-4. Increases of surface area contacting to

supporting bone might improve stress distribution5, so the implants with various size

and length have been developed as well as rough surface architecture. Recently, many

studies reported no significant effect of implant length over 10mm on the survival

rates6-8, whereas that of implant diameter is still controversial.

Some specific conditions restricting placement of a standard or wide implant are

often encountered; severe alveolar bone defect, narrow ridge9 or mesio-distal span10, 11.

Chronic pathologic conditions including endodontic and periodontal problem12 result

in a severe bone defect, even natural healing itself can make a narrow alveolar ridge

in anterior teeth area13, 14.

Several advanced surgery techniques; guided bone regeneration technique9,

distraction osteogenesis15, and autogenous bone graft16 have been reported to

overcome these deteriorated conditions, and were used successfully in the clinical

dental fields. However, supporting effect of regenerated alveolar bone around dental

implants is questionable to be the same as native alveolar bone17. In addition, these

advanced augmentation surgeries have some disadvantages, such as prolonged

healing time, additional cost, and unpredictable complications included infection and

wound exposure18. So, in some cases, using a narrow implant within the native

alveolar bone can be better than making a dehiscence defect around a wider implant

in the aspect of the support and control of the risk.

On inserting implant fixture in a ridge of narrow mesio-distal span, using a

standard implant can cause damage on the neighboring root. In addition, replacement

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of the incisors except for maxillary central incisor by standard implants can result in

esthetically unpleasant outcome, because of smaller width of tooth cervix compared

to the implant. On the other hand, use of a narrow implant might reduce the

prevalence of these problems.

In spite of these advantages of narrow implant, there are several inadequacies to

replace routinely standard implant with narrow one. First, thin fixture wall around

abutment or screw, which was made by reduced diameter of implant, can increase the

risk of fracture of implant fixture and screw19. In addition, a decreased proportion of

implant diameter to occlusal surface can increase cantilever effects, which increase

the risk of overload.

Many reports stated that the cumulative survival rates of narrow implants were

similar to those of standard implants20-22. However, there were few studies focused on

evaluating their long-term results of multiple implant systems21. So it is hard to make

and confirm the consensus of this issue.

The objective of this study was to evaluate the long-term cumulative success rate

of narrow implant of various systems, and analyze biological and mechanical

complications.

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Ⅱ. MATERIALS AND METHODS

This study was performed as a retrospective analysis of patients treated in the

Department of Periodontology, Dental Hospital of Yonsei University (Seoul, Korea)

and comprised of a total of 541 narrow implants in 338 patients (154 men and 184

women), who were aged between 20 and 85 years (average 52.5 years; Table 1).

These fixtures had been consecutively installed between May, 1995 and April, 2009.

This retrospective study was approved by the Institutional Review Board at Yonsei

Dental Hospital (deliberate number 2-2011-0002).

The medical history of each patient was assessed for current and previous

diseases, and only healthy patients were included in the study. In addition, patients

who had any of the following conditions were excluded: (1) psychological disorder;

(2) uncontrolled Diabetes Mellitus; (3) immune suppression; (4) bisphosphonate

medication; (5) previous radiotherapy to the head and neck region; (6) treatment of

anti-blastic chemotherapy; (7) parafunctional oral habits such as clenching and

bruxism; (8) pregnancy; (9) untreated periodontitis in neighboring teeth; (10) the age

of under 20 years.

Of 541 narrow implants that were placed, 290 (53.6%) were inserted in the

maxilla and 251 (46.4%) were inserted in the mandible. In addition, 386 (71.3%)

implants were inserted in the anterior region and 155 (28.7%) implants were inserted

in the posterior region. Five implant systems were used in this study and the

distributions were as follows: 222 Replace Select® (Gothenberg, Sweden), 149

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Brånemark® (Gothenberg, Sweden), 61 Implantium® (Seoul, Korea), 58 Xive®

(Mannheim, Germany), and 51 Straumann® (Basel, Switzerland) implants. The

diameters and lengths of implants used in this study were shown in Table 2.

Advanced bone augmentation surgeries were taken additionally in some cases of

severely resorbed alveolar ridge; guided bone regeneration around 214 implants and

ridge splitting with 20 implants. Bone qualities of alveolar ridge were distributed by

the tactile evaluation of surgeon, based on the classification of Lekholm and

Zarb23(Table 3).

All implants in this study were used for fixed prosthesis. 365 implants were

splinted with the neighboring implants and 176 implants were restored without

splinting. The prostheses were distributed into two types; screw-type (107 implants)

and cement-type (422 implants). However, 12 implants remained unknown due to a

lack of information about their prosthesis (Table 4).

Changes of peri-implant marginal bone level were measured on periapical

radiographs, which were taken immediately after installation and the last follow-up

visit, using the image analysis software (Starpacs® System, Infinitt Co.,LTD, Seoul,

Korea). After length calibration using a known fixture length, bone level was

measured from the top of the implant fixture to the most crestal point of bone-to-

implant contact. Mean marginal bone level (MMBL) was averaged of both mesial and

distal sides of an implant, and annual marginal bone level change (AMBC) was taken

by dividing the difference between MMBLs of two measuring times by observation

periods.

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The criteria for success proposed by Buser et al. and Cochran et al. was used24-26;

absence of clinically detectable implant mobility, absence of pain or subjective

sensation, absence of recurrent peri-implant infection, and absence of continuous

radiolucency around the implant. In case of implant removal, implants were classified

as ‘failures’. Implants with progressive marginal bone loss still used were regarded as

‘ailing implants’.

Cumulative success and survival rates were evaluated using time-related survival

probabilities according to Kaplan & Meier (SPSS), and log rank test and ² test ( <

0.05) were used for the comparison of the survival rates between the subgroups.

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Ⅲ. RESULTS

Results of Kaplan-Meier survival and success estimates

Nine patients with 12 implants were dropped out from the follow-up evaluations due

to moving out of the areas, lack of attending in treatments and no response to call. All

these implants were successfully integrated, as documented at the last regular

examination. A total of 329 patients, representing 529 implants were evaluated (range:

1-12 years, mean follow-up time: 4.9 years, follow-up time after prosthesis delivery:

3.9 years) and 9 implants failed during the period of observation.

The cumulative survival rates were 98.1% (Fig. 1) and 98.5% for the implant-

and subject-based analysis respectively and comparisons of survival rates in relation

to various allocations were shown in Table 5. There were no statistically significant

effects of alveolar bone quality, implant locations, gender, age, prosthetic type, and

implant length.

The cumulative success rates were 91.8% (Fig. 2) and 93.8% for the implant-

and subject-based analysis respectively. There was significant difference between the

success rates of implants in relation to patient’s age (p=0.03; Fig. 3). The older

patients group, the lower success rates were shown except the 70’s group (20’s:92.9%,

30’s:97.2%, 40’s:93.3%, 50’s:89.4%, 60’s:85.2% and over 70’s:97.9%). In addition,

there was a tendency of decreasing success rate in bones of a low density (Fig. 4) and

five implant systems showed heterogenous success rates (83.7~100%), although there

were not statistically significant differences (Fig. 5). There were also no significant

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effects of implant locations, gender, prosthetic type, and implant length on success

rates.

Radiographic analysis

Annual marginal bone loss between implant insertion and follow-up visit was 0.07 ±

0.2mm (0.08mm at mesial; 0.07mm at distal side of the implants). There were 24

ailing implants, which were composed of fifteen in the maxilla and nine in the

mandible. There were 15 implants in the anterior teeth area and 9 implants in the

posterior teeth area. The mean marginal bone loss around the ailing implants was

2.74mm.

Complications

Table 6 shows the types and numbers of complications classified with two groups,

such as biological and mechanical complications.

Biological complications

Among 14 biological complications, 8 implants were positioned in the maxilla

(anterior-7; posterior-1), while 6 implants were positioned in the mandible (anterior-4;

posterior-2). There were swelling, wound dehiscence, fistula formation, infection and

pus discharge according to biological complication. The infection was the highest

reason of the biological complication.

Mechanical complications

The mechanical complications occurred in 54 implants. Thirty-four implants were

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placed in the maxilla (anterior-28; posterior-6), and twenty implants in the mandible

(anterior-13; posterior-7). The mechanical complications can be classified with

decementation, screw loosening, porcelain fracture and implant fracture. The most

frequent mechanical complication was the decementation. Screw loosening occurred

in 15 implants and porcelain fracture was also observed in 9 implants.

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IV. DISCUSSION

The locations placed narrow implants in this study were concentrated in anterior

area, especially lateral incisors (Mx:137, Mn:92). This concentration-of-distribution

might result from mainly severe labial bone resorption after tooth extraction. Block et

al.27 stated that there was accompanying horizontal deficiency in more than 50% of

anterior sites when a delayed approach, due to very thin labial bone. On an implant

insertion surgery at a severely resorbed ridge, there can happen a large dehiscence

defect around the fixture using standard or wide implant18. Even in cases having

resorption of both labial and palatal (lingual) bone, using a wider implant can make

difficulties to take initial stability due to a large defect around the fixture.

These cases needed advanced surgery techniques like GBR and ridge splitting to

prevent or treat defects around implant9. However, the problem is a complication

accompanied with these techniques. In a recent systematic review article, authors

reported infection and membrane exposure in 20% non-resorbable membranes and

5% resorbable ones during post-operative period. Of 214 cases using a membrane in

this study, just 2 cases showed infection sign and were removed all the implants and

graft materials. Using a narrow implant in a resorbed ridge appeared decreasing a risk

of complication associated with a membrane, by decreasing a necessary volume of

graft, as well as diminishing the need for graft by obviating the defect.

Of nine failed implants in the present study, 7 implants are categorized into early

failure; 4 infections without osseointegration, 2 infections associated GBR, and a case

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of failure of osseointegration. Only two implants of a total 541 implants were

removed due to late failure; both were screw fractures. Previous studies reported the

fracture rates of 0.67% 22 and 0.26% 20 and the result of this study (0.03%) was in

agreement with these. It has been concerned that the increase of occlusal forces in the

posterior area might cause fractures of narrow implants 28. In contrast to concerns of

narrow implants, only two screw fractures occurred in the anterior maxilla. In

addition, these two implants were an external connection system, which screw

loosening could happen more easily.

The mechanical complications (n=54) were observed more than the biological

complications (n=14), which is consistent with the results of the previous studies29-31.

Decemetation and screw loosening were first and second highest reasons among

mechanical and biological complications, respectively. Arisan et al.29 stated that

reduced the abutment surface and cement retention area of narrow implants might

increase the chance of cement loosening. Splinting with neighboring implants was

recommended for this reason, however in the present study, decementations in a type

of splint prosthesis (19 implants / total 365) occurred in a similar rate compared to

single implants (9/176). In addition, all 15 screw loosening were in the splint

prostheses.

Another reasons of these complications might be fatigue from the occlusal forces

and parafunctional habits, framework misfit, or unfavorable leverage32,33. The

complications of this study could be more associated with loading problems rather

than decreased surface of narrow implants.

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Previous studies reported no statistical differences when cumulative survival and

success rates of narrow implants were compared with those of standard implants20, 21

as well as wide implants1. These were in agreement with the result of this study;

survival rates (98.1%) and success rates (91.8%). However, on the contrary to the

other previous studies34-37, this study showed a tendency of decreasing success rates in

relation to aging (p=0.03). The difference of the present study from the others is

specific focus on the narrow implant and the age. Stress values and concentration

areas increased for cortical bone when implant diameter decreased38, 39, so occlusal

force via narrow implant might affect the crestal bone loss of older patients, who

having a weaker remodeling potency.

In addition, the difference of implant design resulted in heterogenous success

rates (83.7~100%; p=0.113). Previous studies of finite element analysis observed the

effect of implant design on distribution of forces and finally marginal bone loss 40, 41.

Because there is possibility of synergism between design and narrow diameter38, 39,

further studies of proper design and materials for narrow implants are necessary.

Taken all together, even though there are some changes of marginal bone in older

patients, the use of narrow implants is recommended in the replacement of teeth with

small cervical diameter or in a severely resorbed ridge.

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V. Conclusion

• The cumulative survival rates were 98.1% and 98.5% for the implant- and

subject-based analysis, respectively. The cumulative success rates were

91.8% and 93.8% for the implant- and subject-based analysis, respectively.

• Narrow implants had high reliability.

• Even though there are some failures and complications, the use of narrow

implants is recommended in the replacement of the teeth with small cervical

and a thin alveolar crest.

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8. C. C. Wyatt and G. A. Zarb, Int J Oral Maxillofac Implants 13 (2), 204-211

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18. M. Chiapasco and M. Zaniboni, Clin Oral Implants Res 20 Suppl 4, 113-123

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TABLES

Table 1. Distribution of implants according to patients’ age and gender

Age (Year) Male Female Total

20-29 28 25 53

30-39 17 32 49

40-49 26 29 55

50-59 47 38 85

60-69 26 34 60

>70 10 26 36

Total 154 184 338

Table 2. Distribution of implants according to diameter and length

Diameter/

Length(mm) 8

9.5

10

11

11.5

12

13

14

15

Total

Ø 3.3 3 0 48 0 45 28 66 1 9 200

Ø 3.4 4 12 21 31 0 34 15 2 0 119

Ø 3.5 0 0 36 0 0 0 186 0 0 222

Total 7 12 105 31 45 62 267 3 9 541

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Table 3. Distribution of bone quality

Bone quality D1 D2 D3 D4 Unknown Total

Maxilla 3 81 168 19 20 291 Mandible 21 134 66 5 24 250

Total 24 215 234 24 44 541

Table 4. Distribution of prosthesis type

Prosthesis type Screw-type Cement-type Unknown Total

Single 19 151 6 176 Splinged 88 271 6 365

Total 107 422 12 541

Table 5. Comparisons of the survival rates and p-values.

Survival rate (%) p-value

Maxilla/Mandible 97.3 / 99.2 0.150

Anterior/Posterior 97.7 / 99.4 0.267

Short/ Long 100 / 98.1 0.593

Screw/Cement 96.9 / 98.3 0.880

Single/Splinted 98.9 / 97.8 0.487

Male/Female 98.3 / 98.0 0.977

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Table 6. Types and Numbers of complications

Types Anterior Posterior Anterior Posterior Total Maxilla Maxilla Mandible Mandible

Biological Infection 3 1 2 0 6

complication Pus discharge 1 0 2 0 3

Fistula formation 1 0 0 1 2

Swelling 2 0 0 0 2

Failure of osseointegration 0 0 0 1 1

Total 7 1 4 2 14

Mechanical Decementation 16 2 10 0 28

complication Screw loosening 7 2 2 4 15

Porcelain fracture 3 2 1 3 9

Implant fracture 2 0 0 0 2

Total 28 6 13 7 54

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FIGURES

◇Fig 1. Kaplan-Meier survival curve of the implants

◇Fig 2. Kaplan-Meier success curve of the implants

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◇Fig 3. Kaplan-Meier success curves for implants according to patient’s age

Fig 4. Kaplan-Meier success curves for implants according to bone quality

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Fig 5. Kaplan-Meier success curves for implants according to implant systems

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국문요약

단폭경 임플란트의 장기간 누적 성공률에 관한 장기간 후향적 연구

<지도교수 채 중 규>

연세대학교 대학원 치의학과

김 현 민

장기간의 성공적인 결과로 인해 임플란트는 구강치료의 한 영역으로

자리를 굳히고 있다. 임플란트 수복은 완전무치악이나 부분무치악

환자에서 높은 성공률을 보이고 있으며, 단일치 임플란트에서도 높은

성공률과 함께 널리 사용되고 있다.

이러한 단일치 임플란트 수복의 경우, 임플란트 직경의 선택은 무치악부의

종류, 잔존골의 양, 보철치료가 가능한 공간, emergence profile 등에

의한다.

발치 후 흡수에 의해 임플란트 식립을 위한 골의 부족이나 치간 사이의

공간 부족 등이 나타날 수 있다.

해부학적으로 하악전치나 상악측절치의 경우 근원심간 거리가 대부분

4.5mm 이하로 이런 부위에 임플란트를 식립 할 경우 심미적으로 만족할

만한 결과를 얻기 위해서는 narrow implant 를 식립하는 것이 유용하다.

이번 연구는 2010년 5월 1일을 기준으로 식립 후 1년이 지난, 즉

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2009년 4월 30일 이전에 식립 된 541개의 narrow implant(직경

3.5mm이하)를 대상으로 연세대학교 치과병원 치주과에서 치료받은

338명의 환자들을 대상으로 분석이 이루어졌다.

결과는 다음과 같다.

총 9 개의 임플란트가 제거되었으며, 그 중 상악에서는 6 개, 하악에서는

3 개가 제거되었다. 임플란트 수를 기초로 한 장기간 누적생존율은 98.1%

(상악: 97.3%, 하악: 99.2%)였으며, 환자수를 기초로 한 장기간

누적생존율을 98.5%였다. 합병증은 총 68 건이 발생되었고, 생물학적

합병증과 기계적 합병증으로 분류되었으며, 기계적 합병증이 생물학적

합병증보다 많이 관찰되었다.

생물학적 합병증으로는 부종, fistula 형성, 감염 등이 있었으며, 그 중에서

감염이 가장 많이 발생되었다. 기계적 합병증으로는 임플란트 파절,

screw 파절, screw loosening, decementation 등이 있었으며, 가장 자주

발생한 합병증은 decementation 이었다.

결론적으로 단폭경임플란트는 감소된 골이나 치간 사이에 만족할 만한

결과를 얻었으며, 적은 합병증과 함께 성공적인 누적성공률을 보였다.

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핵심되는 말: 단폭경 임플란트, 누적성공률, 합병증

long-term retrospective study of narrow implants; 1-12 ... · cumulative survival rate and success...

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