The Amount of Wear in Attachment of Implant-Supported Overdentures in Mandible

Document Type: Original Article

Authors

1 Associated Professor, Department of Prosthodontics, Dental Research Center, Faculty of Dentistry, Hamadan University of Medical Sciences, Hamadan, Iran

2 Resident of Prosthodontics, Department of Prosthodontics, Faculty of Dentistry, Hamadan University of Medical Sciences, Hamadan, Iran

3 Assistant Professor, Department of Prosthodontics, Dental Research Center, Faculty of Dentistry, Hamadan University of Medical Sciences, Hamadan, Iran

4 Assistant Professor, Department of Prosthodontics, Dental Research Center, Faculty of Dentistry, Zahedan University of Medical Sciences, Zahedan, Iran.

5 Assistant Professor, Department of Biostatistics, Faculty of Health, Hamadan University of Medical Sciences, Hamadan, Iran

6 Resident of Prosthodontics, Department of Prosthodontics, Faculty of Dentistry, Hamadan University of Medical Sciences, Hamadan, Iran.

7 Assistant Professor, Department of Periodontology, Implant Research Center, Faculty of Dentistry, Hamadan University of Medical Sciences, Hamadan, Iran.

Abstract

Background and objectives: One of the simplest and cheapest attachments for overdentures, is the ball-type attachment, however, keeping it during the first year of prosthesis delivery and after that is one of the main concerns of dentists. The present study aimed to assess the wear of matrix in overdentures attachment supported by one, two and three implants in the mandible.
Materials and methods: Thirty edentulous patients were randomly divided into three groups: the first group received a single implant in the midline of the lower mandible, the second group two implants in areas B and D, and the third group three implants in areas B, C, and D. The attachment used in patients’ prosthetic with single and two implants was O-ball/ring attachment and for patients with three implants, the treatment plan was ball bar-supported attachments. After placing the new matrix implant for each patient and obtaining their consent, the matrix wear was measured with CMM (Coordinate Measuring Machine) device. To compare matrix wear after six months and one year, measurements were repeated. Data analysis, using ANOVA and multiple comparisons was down by Tukey Test. variance with repeated measures and Tukey test were used to compare the groups two-by-two. P.value less than 0.05 was set statistical significant. SPSS 16 software was used for data analysis. Results: The data obtained from the CMM device showed that the lowest mean matrix wear in the maximum single implant and maximum mean were in group two. Conclusion: Both time and the number of implants had a significant effect on the wear of the O-ring.

Keywords

Main Subjects


Introduction

Overdenture is a mobile partial or complete prosthesis, supported by one or more remaining teeth and dental implant. Alveolar ridge protecting prosthesis is inherently unstable. Due to the unpredictable bone loss, preserving the stability of the prosthesis is negatively affected and most of these problems will appear in the lower arch or mandible. The data indicate that edentulous patients generally have medium level of incomes and because of this; the cost of treatment is an important determinant in compliance for implants. Therefore, the price between 1 and 2 and 3 implants will be different from surgical and prosthetic perspectives. One of the easiest and cheapest attachments for overdenture is ball-type attachment but keeping it in the first year of prosthesis delivery and after that is one of the main concerns of dentists. Over time, the clinical use of denture results in attachment wear which reduces the retention, declining stability and patient satisfaction (1-4). The cost of treatment is, on the other hand, one of the key factors in choosing overdenture treatment that affect the treatment planning for patients and the number of implants (5-6). Replacing the components of matrix of the attachment is necessary for patient satisfaction from the denture’s retention (7-8). So far, there are few studies focusing on measuring the lifetime of the attachment’s components and comparing the number of implants in a group of patients, the present study aimed to evaluate the wear of attachment of overdentures supported by one, two, and three implants in the mandible. A study by Gotfredson et al. in 2000 showed that two implant-supported overdentures with bar or ball attachment has a whole 5-year survival rate and there was no difference in marginal bone loss and health of mucosa near the implant between bar and ball attachment, but the technical problems and repair for each patient was 20 times higher in bar system than the ball-type attachment (20). Karabuda and colleagues evaluated and compared the prosthetic problems of patients with 2 to 4 implants splintedwith a round bar and patients with 2 to 4 implants with ball attachment in a clinical study in 2008. Their results showed no difference for prosthetic problems between the two attachment systems and both were introduced as a reliable method for the treatment of edentulous patients21. Roberto Branchi and colleagues evaluated the resistance to wear in four matrices of ball attachment for implant-supported overdentures in their laboratory in 2009. According to their results, matrices made of gold and teflon had the highest retention without reduction after 3 years of use, whereas titanium and O-ring matrix showed a steady decline in retention (22). Kleis and colleagues conducted a one-year clinical evaluation in 2010 to compare three different attachment systems (locator, ball attachment with gold matrix, ball attachment with rubber O-ring) for two-implant supported overdenture. They reported a loss of retention. During the study, the                                                                                                                                                                                                                                                       Locator system showed a higher maintenance compared to ball systems, but oral health-related quality of life did not differ in any of the three attachment systems23. Olivier Fromentin et al. studied the clinical wear of ball attachments after one, three, and eight years in 2011and reported that there was a significant reduction in diameter of all group compared to the control group and the highest rate of wear was obtained after three years of clinical use (24). In 2011, Alsabeeha and colleagues compared three systems used for implant-supported overdenture attachment (ball attachment made of titanium-nitride with plastic matrix, uncoated titanium ball attachment with Della Bone-type gold alloy matrix, and Locator made of titanium-nitride and plastic matrix) regarding wear characteristics and deformation after one year and showed that among the three systems, ball attachment made of titanium-nitride with plastic matrix had a better wear characteristics and clinical behavior; and the authors recommended it for single implant overdentures 25. The results of the study by Olivier Fromentin et al. in 2012, which examined the wear of matrix ball-shaped attachment over one and eight year(s), showed that after one year of clinical use, wear had a little effect on matrix attachments, while the results of three to eight years showed a significant reduction in the thickness of the matrix26. In another study in 2012, the wear of ceramic and titanium attachments was clinically evaluated and the least wear was observed in attachments with ceramic matrix, but using ceramic attachments was not recommended because of higher rate of fracture (27). The aim of this study is to evaluate the amount of wear in attachment of implant-supported overdentures in mandible.

 

Materials and methods

In this in vitro experimental study, 30 fully edentulous patients with a mean age of 59 years, being edentulous in the mandible arch for at least one year and treated under overdenture implant participated. Data was collected through observation and checklist. Patients were divided into three groups: the first group, a plate form 3.8-mm implant (Implantium, II SOFX 483810R, South Korea) in midline of mandible, in the second group, two implants in areas B and D with the same diameter and brand were placed. Attachment systems used for both groups of patients were O-ring and metal housing (Implantium, SOBA 4800 simple line II South Korea) (Fig 1 and 2).

 

 

 

 

 

 

 

 

 

 

Figure 1.The sample used in the study

 

 

 

 

 

 

 

 

 

Figure 2. The sample used in the study

 

The third group had three implants in areas B, C, and splinted by a metal bar-shaped frame and two ball-shaped attachments between implants. Denture of patients consisted of supra structure with two metal housing and the nylon cap. All patients used simple completed denturesin the maxillary. After placing the new matrix (O-ring) in prosthesis of each patient, with the consent of the patient, samples were sent to the laboratory to measure the amount of wear in the matrix as measured by the coordinate measuring machine (LH87; Wenzel, Germany). Metro soft 3.60 Software was used in this device and the measuring range was 800 × 1000 × 700 mm (Fig. 3).

 

 

 

 

Figure 3. DeviceCMM

The device probe can determine coordination at the center of each circle than the standard sphere, and amount of out of circularity (OC); that is the difference between surface points of the measured circle and an ideal circle with similar radius (Fig. 4).

 

 

 

 

 

 

 

 

 

 

 



Figure 4.Sizes obtained by CMM devices related to Overdenture matrix of implant based on two measurements in one-step

 

 

After six months of using each denture, patients were followed for periodic assessment and their dentures measured for the amount of matrix wear for the second time using the CMM (Coordinate Measuring Machine). These assessments were repeated for a third time after six months and if needed, matrices were replaced. The pattern of wear was determined through direct observation of matrices. Finally, to summarize the collected data, descriptive statistics including charts, tables and numerical indexes were used. In addition, for data analysis, using ANOVA and multiple comparisons was down by Tukey Test. variance with repeated measures and Tukey test were used to compare the groups two-by-two. P.Value less than 0.05 was set statistical significant. SPSS 16 software was used for data analysis.

 

Results

The data obtained from the CMM device showed the lowest mean matrix wear in single implant and the maximum wear in the group with two implants.

Finding worn out O-ring and comparing them with healthy figures showed that almost half of the samples with single and two implants had installation damage that caused the O-ring to tear and scale. This type of wear, which is a common problem, determined with short cuts notch and scaling. The causes of problems of sharp edges on the encapsulator are due to improper laboratory procedures, sharp edges on the ball and large size O-ring, O-ring rotation in encapsulator, small-sized O-ring for ball or insufficient sliding of the O-ring during placement. Suggested solutions include using appropriate size of the O-ring and lubricant (Table 1; Fig. 5 and 6).

 

 

 

 

 

 

 

 

 

                                                                                                          Figure 5.View from the O-ring normal

 

 

 

 

 

Table 1. Descriptive statistics wear the Matrix Based on the number of implants and Time

Time

Implant

Number

Average

Standard deviation

Normal

1

10

14854.1

220.4

2

10

21910.8

2585.4

3

10

19916.2

1746.3

Total

30

18893.7

3484.5

6 months

1

10

17265.7

1373.9

2

10

23913.4

1704.2

3

10

21851.2

1767.4

Total

30

21010.1

3231.4

one Year

1

10

17498.5

1485.3

2

10

24538.7

1721.2

3

10

22980.6

1762.5

Total

30

21672.6

3463.9

 

 

 

 

Figure 6.View of the wear of Installation and Spiral

 

In other combinational cases, extrusion and spiral damage were observed. Comparing nylon cap used in the prosthesis supported by three implants in more than half of the samples, a combination of abrasion and compression set were observed (Table 2 and 3; Fig. 7)

 

 

 

Figure 7.View of nylon cap worn Rhine

 

 

 

 

 

 

Table 2.Analysis of variance with repeated measures

Sum of Squares

Degrees of freedom

Mean Square

F

P.value

Resource change

37916530369.6

1

37916530369.6

5442.2

<0.001

Time

767525948.1

2

383762974.1

55.1

<0.001

Implant



Table 3.Wear resistance of the matrix in over denture implant over time.

 

Time

Time

Mean difference(i-j)

P.value

Overdentures based on 1 implant

Normal

6 months

-2411.6

0.0006

One year

-2644.4

0.0005

6 months

One year

-232.8

0.0084

Overdentures based on 2 implant

Normal

6 months

-2002.6

0.0020

One year

-2627.9

0.0019

6 months

One year

-625.3

0.0059

Overdentures

Normal

6 months

-1935

0.003

based on 3 implant

 

One year

-3064.4

0.002

6 months

One year

-1129.4

0.0011

 

 

 

 

Discussion

 In the in vitro study, conducted by Branchi in 2009 where 4 Matrix types with ball attachment were compared, it was observed that O-ring matrix had a progressive decrease in retention up to 1600 cycles (insertion and removal) and then the retention remained stable. After approximately 500 cycles, the retention reached below the theoretical limit (0.5 kg) in order to ensure acceptable prosthesis retention. He considered that reduced retention was due to lower modulus of elasticity in O-ring matrix (22). According to research findings, a patient takes out the denture almost 3 times a day. Thus, 1000 cycles of wear test is equal to one year of clinical use of denture28-30. In patients of the present study, similar to Branchi’s study, a progressive reduction in retention was observed during one year, but not all patients were dissatisfied with denture retention; it should be noted that the study conducted by Branchi was in vitro, whereas patient satisfaction from treatment and retention of denture is a complex and multifactorial phenomenon and does not just depend on biomechanical factors.

The results of the study by Aslabeeha during one year on single implant-supported overdentures to compare retention and deformation of four different types of attachments showed that the minimum retention and maintenance were in plastic matrix with 2 replacements in 12 patients which confirm the results of the current clinical study (25). Oliver Fromentin showed in a study in 2012 that many factors such as attachment angulation to the occlusal plane, inter implant angulation, different routes of insertion and removal, muscle strength and chewing habits are effective on the amount of retention. Denture stability is also an important factor affecting the retention26. Perhaps one important factor in increasing retention in overdentures supported by two and three implants in the present study was harder control of attachment angulation to the occlusal plane and inter implant angulation. On the other hand, it seems that increase in the stability of the implants supported by three implants reduces the influence of other variables in matrix retention. The reason for differences in the type of retention in the two types of O-ring is related to the difference in the material of O-ring and the type of ball system used. Single and two implant systems in ball attachment and ready housing are used with a polished surface, while the attachment system supported by three implants is made of castableball and bar. The nylon caps used in prostheses supported by three implants in more than half of the samples as a combination of abrasion and compression set were compared. In abrasion, thinner surface of the O-rings are smooth and rubbed; one of the reasons for this is the rough surface of metal ball that acts as abrasive. It is suggested to use more resistant O-ring to fix the problem of surface wear. In compression type, smooth surfaces are created in both sides of the O-ring. The common reason for this problem is parafunctional clenching on the prosthesis. Other reasons include using elastomer with improper compression characteristics or bites on the prosthesis to place prostheses. The proposed solution is to take the prosthesis out from the mouth during the night and reduce the hardness of the O-ring(19). Finding worn out O-ring and comparing them with healthy figures showed that almost half of single and two samples had installation damage. The causes of the problems include large size of O-ring,, O-ring rotation in encapsulator,  small O-ring for ball or inadequate sliding of the O-ring during placement. It seems that due to the structural form of Implantium, O-ring has more elasticity than the Rheinnylone cap, thus it increases the likelihood of O-ring rotation. Suggested solutions include using appropriate size of the O-ring and lubricant.

 

Conclusion

Time and the number of implants, both had a significant effect on the O-ring wear. Among the three groups in the study, the lowest rate of retention was in the group with single implant.

References

  1. Den Dunnen AC, Slagter AP, de Baat C, Kalk W. Professional hygiene care, adjustments and complications of mandibular implant-retained overdentures: a three-year retrospective study. The Journal of prosthetic dentistry. 1997 Oct 31; 78(4):3873-90.
  2. Cooper LF, Scurria MS, Lang LA, Guckes AD, Moriarty JD, Felton DA. Treatment of edentulism using Astra Tech implants and ball abutments to retain mandibular overdentures. International Journal of Oral and Maxillofacial Implants. 1999 Sep 1; 14(5):646-653.
  3. Sadowsky SJ. Mandibular implant-retained overdentures: a literature review. The Journal of prosthetic dentistry. 2001 Nov 30; 86(5):468-473.
  4. Van Kampen F, Cune M, Van Der Bilt A, Bosman F. Retention and postinsertion maintenance of bar‐clip, ball and magnet attachments in mandibular implant overdenture treatment: an in vivo comparison after 3 months of function. Clinical oral implants research. 2003 Dec 1; 14(6):720-726.
  5. Meijer HJ, Raghoebar GM, Van‘t Hof MA. Comparison of implant-retained mandibular overdentures and conventional complete dentures: a 10-year prospective study of clinical aspects and patient satisfaction. International Journal of Oral & Maxillofacial Implants. 2003 Nov 1; 18(6), 879-885
  6. Timmerman R, Stoker GT, Wismeijer D, Oosterveld P, Vermeeren JI, Van Waas MA. An eight-year follow-up to a randomized clinical trial of participant satisfaction with three types of mandibular implant-retained overdentures. Journal of dental research. 2004 Aug 1; 83(8):630-633.
  7. Holst S, Blatz MB, Eitner S, Wichmann M. In vitro wear of different material combinations of intracoronal precision attachments. International Journal of Prosthodontics. 2006 Jul 1; 19(4).
  8. Wolf K, Ludwig K, Hartfil H, Kern M. Analysis of retention and wear of ball attachments. Quintessence international. 2009 May 1; 40(5):405-412.
  9. Albrektsson T, Zarb G, Worthington P, Eriksson AR. The long-term efficacy of currently used dental implants: a review and proposed criteria of success. Int J Oral Maxillofac Implants. 1986 Jan; 1(1):11-25.
  10. Cordioli G, Majzoub Z, Castagna S. Mandibular overdentures anchored to single implants: a five-year prospective study. The Journal of prosthetic dentistry. 1997 Aug 31; 78(2):159-165.
  11. Liddelow GJ, Henry PJ. A prospective study of immediately loaded single implant-retained mandibular overdentures: preliminary one-year results. The Journal of prosthetic dentistry. 2007 Jun 30; 97(6):S126-37.
  12. Liddelow G, Henry P. The immediately loaded single implant-retained mandibular overdenture: a 36-month prospective study. International Journal of Prosthodontics. 2010 Jan 1; 23(1):13.
  13. Kronstrom M, Davis B, Loney R, Gerrow J, Hollender L. A prospective randomized study on the immediate loading of mandibular overdentures supported by one or two implants: a 12-month follow-up report. International Journal of Oral & Maxillofacial Implants. 2010 Jan 1; 25(1).
  14. Kronstrom M, Davis B, Loney R, Gerrow J, Hollender L. A Prospective Randomized Study on the Immediate Loading of Mandibular Overdentures Supported by One or Two Implants; A 3 Year Follow‐Up Report. Clinical implant dentistry and related research. 2014 Jun 1; 16(3):323-329.
  15. Naert I, Alsaadi G, Quirynen M. Prosthetic aspects and patient satisfaction with two-implant-retained mandibular overdentures: a 10-year randomized clinical study. International Journal of Prosthodontics. 2004 Jul 1;17(4), 401-410
  16. Kline R, Hoar JE, Beck GH, Hazen R, Resnik RR, Crawford EA. A prospective multicenter clinical investigation of a bone quality-based dental implant system. Implant dentistry. 2002 Sep 1; 11(3):224-34.
  17. Engquist BO, Bergendal T, Kallus T, Linden U. A retrospective multicenter evaluation of osseointegrated implants supporting overdentures. International Journal of Oral & Maxillofacial Implants. 1988 Jun 1; 3(2).
  18. Bergendal T, Engquist B. Implant-supported overdentures: a longitudinal prospective study. International Journal of Oral and Maxillofacial Implants. 1998 Mar 1; 13(2):253-262.
  19. Misch CE. Available bone and dental implant treatment plans. Dental Implant Prosthetics. 2014 Jul 21:315
  20. Gotfredsen K, Holm B. Implant-supported mandibular overdentures retained with ball or bar attachments: a randomized prospective 5-year study. International Journal of Prosthodontics. 2000 Mar 1; 13(2), 125-130
  21. Karabuda C, Yaltrk M, Bayraktar M. A clinical comparison of prosthetic complications of implant-supported overdentures with different attachment systems. Implant dentistry. 2008 Mar 1; 17(1):74-81.
  22. Branchi R, Vangi D, Virga A, Guertin G, Fazi G. Resistance to wear of four matrices with ball attachments for implant overdentures: a fatigue study. Journal of Prosthodontics. 2010 Dec 1; 19(8):614-619.
  23. Kleis WK, Kämmerer PW, Hartmann S, Al‐Nawas B, Wagner W. A Comparison of Three Different Attachment Systems for Mandibular Two‐Implant Overdentures: One‐Year Report. Clinical implant dentistry and related research. 2010 Sep 1; 12(3):209-218.
  24. Fromentin O, Lassauzay C, Nader SA, Feine J, de Albuquerque Jr RF. Clinical wear of overdenture ball attachments after 1, 3 and 8 years. Clinical oral implants research. 2011 Nov 1;22(11):1270-1274.
  25. Alsabeeha NH, Swain MV, Payne AG. Clinical performance and material properties of single-implant overdenture attachment systems. International Journal of Prosthodontics. 2011 May 1; 24(3).247-254
  26. Fromentin O, Lassauzay C, Nader SA, Feine J, Rubens F. Wear of matrix overdenture attachments after one to eight years of clinical use. The Journal of prosthetic dentistry. 2012 Mar 31; 107(3):191-198.
  27. Büttel AE, Lüthy H, Sendi P, Marinello CP. Wear of ceramic and titanium ball attachments in subjects with an implant-retained overdenture: a controlled clinical trial. The Journal of prosthetic dentistry. 2012 Feb 29; 107(2):109-113.
  28. Rutkunas V, Mizutani H, Takahashi H. Influence of attachment wear on retention of mandibular overdenture. Journal of oral rehabilitation. 2007 Jan 1; 34(1):41-51.
  29. Bayer S, Grüner M, Keilig L, Hültenschmidt R, Nicolay C, Bourauel C, Utz KH, Stark H. Investigation of the wear of prefabricated attachments-An in vitro study of retention forces and fitting tolerances. Quintessence International. 2007 May 1; 38(5).
  30. Bayer S, Steinheuser D, Grüner M, Keilig L, Enkling N, Stark H, Mues S. Comparative study of four retentive anchor systems for implant supported overdentures–retention force changes. Gerodontology. 2009 Dec 1; 26(4):268-272.

 

 

 

References

  1. Den Dunnen AC, Slagter AP, de Baat C, Kalk W. Professional hygiene care, adjustments and complications of mandibular implant-retained overdentures: a three-year retrospective study. The Journal of prosthetic dentistry. 1997 Oct 31; 78(4):3873-90.
  2. Cooper LF, Scurria MS, Lang LA, Guckes AD, Moriarty JD, Felton DA. Treatment of edentulism using Astra Tech implants and ball abutments to retain mandibular overdentures. International Journal of Oral and Maxillofacial Implants. 1999 Sep 1; 14(5):646-653.
  3. Sadowsky SJ. Mandibular implant-retained overdentures: a literature review. The Journal of prosthetic dentistry. 2001 Nov 30; 86(5):468-473.
  4. Van Kampen F, Cune M, Van Der Bilt A, Bosman F. Retention and postinsertion maintenance of bar‐clip, ball and magnet attachments in mandibular implant overdenture treatment: an in vivo comparison after 3 months of function. Clinical oral implants research. 2003 Dec 1; 14(6):720-726.
  5. Meijer HJ, Raghoebar GM, Van‘t Hof MA. Comparison of implant-retained mandibular overdentures and conventional complete dentures: a 10-year prospective study of clinical aspects and patient satisfaction. International Journal of Oral & Maxillofacial Implants. 2003 Nov 1; 18(6), 879-885
  6. Timmerman R, Stoker GT, Wismeijer D, Oosterveld P, Vermeeren JI, Van Waas MA. An eight-year follow-up to a randomized clinical trial of participant satisfaction with three types of mandibular implant-retained overdentures. Journal of dental research. 2004 Aug 1; 83(8):630-633.
  7. Holst S, Blatz MB, Eitner S, Wichmann M. In vitro wear of different material combinations of intracoronal precision attachments. International Journal of Prosthodontics. 2006 Jul 1; 19(4).
  8. Wolf K, Ludwig K, Hartfil H, Kern M. Analysis of retention and wear of ball attachments. Quintessence international. 2009 May 1; 40(5):405-412.
  9. Albrektsson T, Zarb G, Worthington P, Eriksson AR. The long-term efficacy of currently used dental implants: a review and proposed criteria of success. Int J Oral Maxillofac Implants. 1986 Jan; 1(1):11-25.
  10. Cordioli G, Majzoub Z, Castagna S. Mandibular overdentures anchored to single implants: a five-year prospective study. The Journal of prosthetic dentistry. 1997 Aug 31; 78(2):159-165.
  11. Liddelow GJ, Henry PJ. A prospective study of immediately loaded single implant-retained mandibular overdentures: preliminary one-year results. The Journal of prosthetic dentistry. 2007 Jun 30; 97(6):S126-37.
  12. Liddelow G, Henry P. The immediately loaded single implant-retained mandibular overdenture: a 36-month prospective study. International Journal of Prosthodontics. 2010 Jan 1; 23(1):13.
  13. Kronstrom M, Davis B, Loney R, Gerrow J, Hollender L. A prospective randomized study on the immediate loading of mandibular overdentures supported by one or two implants: a 12-month follow-up report. International Journal of Oral & Maxillofacial Implants. 2010 Jan 1; 25(1).
  14. Kronstrom M, Davis B, Loney R, Gerrow J, Hollender L. A Prospective Randomized Study on the Immediate Loading of Mandibular Overdentures Supported by One or Two Implants; A 3 Year Follow‐Up Report. Clinical implant dentistry and related research. 2014 Jun 1; 16(3):323-329.
  15. Naert I, Alsaadi G, Quirynen M. Prosthetic aspects and patient satisfaction with two-implant-retained mandibular overdentures: a 10-year randomized clinical study. International Journal of Prosthodontics. 2004 Jul 1;17(4), 401-410
  16. Kline R, Hoar JE, Beck GH, Hazen R, Resnik RR, Crawford EA. A prospective multicenter clinical investigation of a bone quality-based dental implant system. Implant dentistry. 2002 Sep 1; 11(3):224-34.
  17. Engquist BO, Bergendal T, Kallus T, Linden U. A retrospective multicenter evaluation of osseointegrated implants supporting overdentures. International Journal of Oral & Maxillofacial Implants. 1988 Jun 1; 3(2).
  18. Bergendal T, Engquist B. Implant-supported overdentures: a longitudinal prospective study. International Journal of Oral and Maxillofacial Implants. 1998 Mar 1; 13(2):253-262.
  19. Misch CE. Available bone and dental implant treatment plans. Dental Implant Prosthetics. 2014 Jul 21:315
  20. Gotfredsen K, Holm B. Implant-supported mandibular overdentures retained with ball or bar attachments: a randomized prospective 5-year study. International Journal of Prosthodontics. 2000 Mar 1; 13(2), 125-130
  21. Karabuda C, Yaltrk M, Bayraktar M. A clinical comparison of prosthetic complications of implant-supported overdentures with different attachment systems. Implant dentistry. 2008 Mar 1; 17(1):74-81.
  22. Branchi R, Vangi D, Virga A, Guertin G, Fazi G. Resistance to wear of four matrices with ball attachments for implant overdentures: a fatigue study. Journal of Prosthodontics. 2010 Dec 1; 19(8):614-619.
  23. Kleis WK, Kämmerer PW, Hartmann S, Al‐Nawas B, Wagner W. A Comparison of Three Different Attachment Systems for Mandibular Two‐Implant Overdentures: One‐Year Report. Clinical implant dentistry and related research. 2010 Sep 1; 12(3):209-218.
  24. Fromentin O, Lassauzay C, Nader SA, Feine J, de Albuquerque Jr RF. Clinical wear of overdenture ball attachments after 1, 3 and 8 years. Clinical oral implants research. 2011 Nov 1;22(11):1270-1274.
  25. Alsabeeha NH, Swain MV, Payne AG. Clinical performance and material properties of single-implant overdenture attachment systems. International Journal of Prosthodontics. 2011 May 1; 24(3).247-254
  26. Fromentin O, Lassauzay C, Nader SA, Feine J, Rubens F. Wear of matrix overdenture attachments after one to eight years of clinical use. The Journal of prosthetic dentistry. 2012 Mar 31; 107(3):191-198.
  27. Büttel AE, Lüthy H, Sendi P, Marinello CP. Wear of ceramic and titanium ball attachments in subjects with an implant-retained overdenture: a controlled clinical trial. The Journal of prosthetic dentistry. 2012 Feb 29; 107(2):109-113.
  28. Rutkunas V, Mizutani H, Takahashi H. Influence of attachment wear on retention of mandibular overdenture. Journal of oral rehabilitation. 2007 Jan 1; 34(1):41-51.
  29. Bayer S, Grüner M, Keilig L, Hültenschmidt R, Nicolay C, Bourauel C, Utz KH, Stark H. Investigation of the wear of prefabricated attachments-An in vitro study of retention forces and fitting tolerances. Quintessence International. 2007 May 1; 38(5).
  30. Bayer S, Steinheuser D, Grüner M, Keilig L, Enkling N, Stark H, Mues S. Comparative study of four retentive anchor systems for implant supported overdentures–retention force changes. Gerodontology. 2009 Dec 1; 26(4):268-272.