The service life of implant-retained overdenture attachment systems

The service life of implant-retained overdenture at tachment systems Monica Nogueira Pigozzo, DDS, MS,a Marcelo Ferraz Mesquita, DDS, MS, PhD,b Guilherme Elias Pessanha Henriques, DDS, MS, PhD,c and Luis Geraldo Vaz, DDS, MS, PhDd Piracicaba School of Dentistry, State University of Campinas (UNICAMP), Piracicaba, São Paulo, Brazil; Araraquara School of Dentistry, São Paulo State University, Araraquara, São Paulo, Brazil Statement of problem. Implant-retained overdentures are a treatment option for patients who are not satisfied with conventional complete dentures. Although implant-retained overdentures are widely used, little data are available or provided by implant manufacturers about retentive strength and wear of attachments. Purpose. The purpose of this study was to evaluate retentive strength and fatigue resistance of 4 overdenture bar-andclip attachment systems. Material and methods. Forty bar-and-clip attachment system specimens were tested (n=10): Conexão Bar Clip (polymer clip), Sterngold Hader Bar (polymer clip), 3i Gold Hader Type Clip (metal clip), or SIN Clipo (metal clip). Specimens immersed in artificial saliva were tested to 5500 cycles at 0.8 Hz using a servohydraulic universal testing machine. Retention strength values (N) were recorded initially and after 1100, 2200, 3300, 4400, and 5500 insertion and removal cycles during the tensile test using a speed of 1 mm/min and a load cell of 1 kN. Data were submitted to a 2-way repeated-measures ANOVA and the Tukey A post hoc test (α=.05). Results. An increase in retention strength values was observed during the fatigue test after 5500 cycles of insertion and removal. No significant difference in retentive strength was observed in the groups using polymer clips (Conexão Bar Clip and Sterngold Hader Bar) (P=.729); the same occurred with metal clip systems (SIN Clipo and 3i Gold Hader Type Clip) (P=.068). The SIN Clipo system demonstrated the smallest retention strength values, which were significantly different from the other 2 attachment systems, the Sterngold Hader Bar (P<.01) and the Conexão Bar Clip (P<.01). Although the 3i Gold Hader Type Clip did not differ significantly, in terms of retentive strength, from the Sterngold Hader Bar (P=.258), its retentive strength was significantly lower than the retentive strength of the Conexão Bar Clip system (P=.030). Conclusions. The systems evaluated demonstrated satisfactory retention for all time periods tested, as retention strengths from 5 to 7 N should be sufficient to stabilize overdentures. No component fracture or compromise in retention was found for any of the systems tested. (J Prosthet Dent 2009;102:74-80)

This study was supported by FAPESP (State of São Paulo Research Foundation), project no. 04/12515-6, and Conexão Sistemas de Proteses, Ltda. PhD student, Department of Prosthodontics and Periodontics, Piracicaba School of Dentistry, State University of Campinas (UNICAMP). b Professor, Department of Prosthodontics and Periodontics, Piracicaba School of Dentistry, State University of Campinas (UNICAMP). c Professor, Department of Prosthodontics and Periodontics, Piracicaba School of Dentistry, State University of Campinas (UNICAMP). d Professor, Department of Dental Materials and Prosthodontics, Araraquara School of Dentistry, São Paulo State University. a

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Clinical Implications

The level of retentive strength and the maintenance of that strength are important considerations in the selection of appropriate attachments for implant-retained overdentures. The attachment systems evaluated in this study displayed satisfactory retention strength values at all cycle periods tested; component breakage was not observed and an increase in retention strength values was demonstrated after fatigue testing. Implant-retained overdentures are an alternative to fixed complete dentures. Financial concerns are often the reason implant treatment is not chosen,1,2 and may be a significant consideration in selecting an implant-retained overdenture rather than a fixed complete denture.3 Other reasons for selecting implant-retained overdentures include patient preference, phonetic enhancement, access for oral hygiene, and situations that may not be feasibly managed with a fixed prosthesis, such as extreme atrophy, poor bone quality, inability to achieve an esthetic result, or severe angulation of the implants.4 An unfavorable ratio of the artificial crown length (from crestal bone to occlusal table) to implant length (from crestal bone to apical implant depth) may also indicate an implant-retained overdenture.4,5 Mechanical attachments supported by tooth roots to enhance the retention and stability of an overdenture have been used for nearly a century. The use of attachments for overdentures originated in Switzerland around 1898, and was popularized 60 years ago by Gilmore.6 Numerous methods of attaching overdentures to natural tooth abutments have been described.7-9 With current advanced and successful techniques for achieving osseointegration, implants in the edentulous mandible have become a viable treatment option for patients not satisfied with conventional complete dentures.10,11 Although implant-retained overdentures are widely used, little data are available or provided by implant manufacturers about retentive

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strengths and wear of attachments. Nevertheless, there is evidence that retention is an important consideration for patient satisfaction. Using a cross-over experimental design, Burns et al12 found a strong patient preference for attachments with superior retention. In a cross-over clinical trial involving patients with overdentures using bar-and-clip, ball, and magnet attachment systems, the bar-andclip system was shown to provide the greatest retention.8 Attachment retention strengths from 5 to 7 N have been shown to be sufficient for implant-retained overdentures during function.13 However, daily wear, from such causes as prosthesis removal and insertion, as well as the oral microbiological environment, could result in a loss of prosthetic component function and consequent failure of the attachment system.14,15 Thus, the purpose of this study was to evaluate and compare the retention strength and fatigue resistance of 4 bar-andclip overdenture attachment systems. The null hypothesis was that there would be no differences among the 4 types of attachment systems evaluated when compared, before and after fatigue testing.

MATERIAL AND METHODS Four bar-and-clip overdenture attachment systems frequently used for the retention of implant-retained overdentures, listed in Table I, were evaluated. The bar-and-clip attachment system was selected for this study, as it is preferred by patients due to its greater retentive strength as

compared with other systems.8 Specimens were immersed in artificial saliva (1.5 mmol/L Ca, 3.0 mmol/L P, 20.0 mmol/L NaHCO3, pH 7.0) and submitted to a mechanical fatigue test with 5500 cycles of insertion and removal (ƒ=0.8 Hz). Retention strength values were recorded 6 times, initially and at 1100, 2200, 3300, 4400, and 5500 cycles. For the remaining cycles, the retention strength values were recorded 5 times, and the mean was calculated. The methodology used in this study follows that of Gamborena et al.16 According to this study, 5500 cycles of fatigue testing correspond to 5 years of usage, which is considered sufficient for prosthesis replacement, based upon an average use value of 3 insertions/removals per day by the patient. For specimen preparation, a single analog base (10 mm in length, platform diameter of 4 mm, Conexão Sistemas de Prótese Ltda, São Paulo, Brazil), formed by 2 parallel implant analogs embedded 22 mm apart17 in a polyvinyl chloride (PVC) cylinder, was used for all specimens, regardless of the attachment systems used. All bars were screwed into this base, invested, and cast with Ni-Cr alloy (Verabond II; Aalba Dent, Inc, Cordelia, Calif ), airborne-particle abraded with 50 µm of aluminum oxide (Williams Co, Buffalo, NY), finished with a diamond particleimpregnated rubber wheel universal polisher (Brasseler USA, Savannah, Ga), and polished with a felt wheel and zinc oxide (Williams Co). Corresponding clips were embedded individually into other cylinders (Fig. 1). All PVC

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Table I. Systems, complete manufacturer information, number of specimens, and component composition and dimensions (n=10)

Systems

Manufacturer Information

Component Composition

Conexão

Conexão Sistemas

polymer clip

Bar Clip

de Prótese Ltda,

(polytetrafluoroethylene)

São Paulo, Brazil

polymer clip

Sterngold

Sterngold Dental,

Hader Bar

Attleboro, Mass

Component Dimensions Distance between Thickness of Retentive Parts Retentive Part Clip Length Bar Diameter of Clips of Clip 7.25 mm

1.8 mm

2.03 mm

1.2 mm

(nylon)

5.0 mm

0.9 mm

1.8 mm

0.6 mm

2.5 mm

1.7 mm

1.7 mm

0.3 mm

2.5 mm

1.5 mm

1.8 mm

0.5 mm

3i Gold Hader

Biomet 3i,

metal clip

Type Clip

Palm Beach

(75% gold/25% silver)

Gardens, Fla SIN Clipo

Sistema de Implante

metal clip

Nacional, São Paulo, (75% gold/25% silver) Brazil

1 Two parallel implant analogs embedded 22 mm apart 2 Specimen placed in MTS 810 universal testing machine. in PVC cylinder; bar screwed into base and clip embedded individually into other PVC cylinder. cylinders (2 cm in height and 3.5 cm in diameter) were filled with autopolymerized acrylic resin (VIPI Flash; VIPI, Pirassununga, Brazil). The clips were embedded according to the manufacturer’s recommendations;

therefore, spacers were used only for the metal clips (SIN Clipo and 3i Gold Hader Type Clip). Before and after specimen preparation, the retentive parts of clips and bar diameters, for all systems, were measured with an

The Journal of Prosthetic Dentistry

electronic digital pachymeter (Starret Indústria e Comércio Ltda, Itu, Brazil) with 0.01-mm precision to detect any deformation in the attachments which occurred during preparation (Table I).

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August 2009 Artificial aging, fatigue, and tensile strength tests were performed using a universal testing machine (MTS 810 Material Testing System; MTS Systems Corp, Eden Prairie, Minn). Component insertion and removal were performed along the long axis of the implant.18-20 A special software (Function Generator; MTS Systems Corp) was used for the aging process. Specimens were placed in the testing machine and subsequently immersed in artificial saliva at room temperature and subjected to 5500 cycles of insertion and removal of components along the long axis of the implant (ƒ=0.8 Hz) (Fig. 2). The retention strength baseline values were considered to be 5 N, as described in the literature for pros-

thesis stability.13 Tensile strength was calculated using software (TestWorks for TestStar software; MTS Systems Corp) and the universal testing machine (MTS 810 Material Testing System; MTS Systems Corp), with a load cell of 1 kN and speed of 1 mm/min-1, to calculate mean retention strength values. The data analysis was performed using statistical software (SPSS for Windows, v. 11.5; SPSS, Inc, Chicago, Ill). Differences among the 4 systems and 6 cycle periods were identified using a 2-way repeated-measures ANOVA, with systems as a between-subjects factor and cycle as a within-subjects factor. In the event of significant differences observed between the means of systems, the Tukey A post hoc test was

used to determine the location of the differences. For differences observed between the means of cycles, the Bonferroni post hoc method was used to determine the location of the marginal differences. The data are presented as means and standard deviations (SDs); all tests were performed at the .05 level of significance.

RESULTS Differences between the 4 barand-clip overdenture attachment systems and the influence of cycle number on retention are presented in Table II. Means, standard deviations, and group differences are presented in Table III. An increase in retention strength during the 5500 cycles of

Table II. Two-way repeated-measures ANOVA table Test Effects

Source

Type III Sum of Squares

Within subject

Cycles

5218

5

1043.5

27.5

<.005

Cycles x systems

699

15

46.6

1.2

.255

Error (cycles)

6842

180

38.0

Intercept

206103

1

206102.7

498.0

<.005

Systems

14276

3

4758.7

11.5

<.005

Error

14900

36

413.9

Between subject

df

Mean Square

F

P

Table III. Mean retention strength values measured in newtons (N) and standard deviations (SDs) Cycles/Systems

ConexãoA

SterngoldA,B

3iB

SIN

0

28.48 (9.10)

22.81 (4.94)

20.60 (8.58)

10.17 (2.80)

1100a

34.37 (8.24)

30.06 (8.40)

27.28 (13.50)

16.74 (4.35)

2200a,b

38.19 (8.78)

34.06 (8.72)

28.52 (10.37)

15.69 (8.26)

3300b,c,d

39.03 (8.44)

37.33 (9.44)

29.82 (12.00)

19.60 (10.99)

4400c,e

42.92 (10.77)

39.09 (9.50)

28.60 (10.75)

19.85 (12.42)

5500d,e

45.27 (11.41)

41.78 (13.55)

28.61 (9.32)

24.45 (16.04)

* Within-subject factor test (test among cycles) ** Between-subject factor test (test among systems) Values followed with same uppercase letters in column do not significantly differ according to Tukey test (P>.05). Values followed with same lowercase letters in row do not differ significantly according to Bonferroni test (P>.05).

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Volume 102 Issue 2 insertion and removal was observed as follows: initial retention strength was significantly lower than for the other cycles (P<.001); 1100 cycles produced significantly lower retention strengths than 3300 (P=.003), 4400 (P=.003), and 5500 (P=.001); 2200 cycles produced significantly lower values than 4400 (P=.007) and 5500 (P=.002). The 1100 cycle group was not significantly different than the 2200 (P=.369). The 2200 cycle group was not significantly different from the 3300 cycle group (P=.052); 3300 was not significantly different from 4400 (P=.556) and 5500 (P=.073); and 4400 was not significantly different from 5500 (P=.137). Although the retentive strength of the Conexão Bar Clip was greater than that of the Sterngold Hader Bar, there was no significant difference in retentive strength between these 2 polymer clip systems (P=.729). The retentive strength of the 3i Gold Hader Type Clip attachments was greater than that of the SIN Clipo system; however, there was no significant difference in retentive strength between these 2 metal clip systems (P=.068). The SIN Clipo system showed the smallest retention strength values, with significant differences compared to the Sterngold Hader Bar (P<.001) and Conexão Bar Clip (P<.001). Although the 3i Gold Hader Type Clip was not significantly different from the Sterngold Hader Bar (P=.258), the retentive strength of the 3i Gold Hader Type Clip system was significantly lower than the retentive strength of the Conexão Bar Clip system (P=.030). Component breakage was not observed, and results show that the systems evaluated displayed satisfactory retention strength values at all cycle periods tested, since retention strengths from 5 to 7 N have been shown to be sufficient to stabilize overdentures.13

DISCUSSION The null hypothesis that there

would be no differences among the 4 types of attachment systems evaluated when compared, before and after fatigue testing, was rejected, as significant differences were observed as retention strength values increased. Walton et al2 measured and compared the retention strength of metal and polymer clips used to retain overdentures. The authors observed a 12% reduction in retention strength when metal clips were used. Breeding5 and Epstein9 also reported reduced retention strength values in components of overdenture attachment systems. However, other studies have indicated that retention strength of overdenture systems can increase rather than decrease. Gamborena et al16 observed increased retention strength values in specimens after 3000 and 3500 insertion/removal cycles, as well as deformation of polymer components observed under microscopic examination. Setz et al14 suggested that an increase in component surface roughness and some intrabuccal conditions could influence results, by causing plastic deformation of components, reduced retention strength, or fractures. These authors observed deformation in the polymer parts of components due to strengths generated during the tests. Thermal expansion in the polymer parts may have occurred.16 This concept explains the increased retention strength values in Table III. When comparing the 4 types of attachment systems, it was observed that there was no significant difference in the polymer clip systems, Conexão Bar Clip and the Sterngold Hader Bar (Table III). Differences in retention strength are likely influenced by individual characteristics, such as clip length, distance between the clip’s retentive parts, bar diameter, and the thickness of the clip’s retentive part. As the thickness of the retentive part increases, the clip will be less flexible; thus, retention will be increased. The Conexão Bar Clip system presented thicker retentive parts than the Sterngold Hader Bar system.

The Journal of Prosthetic Dentistry

Moreover, the clip of the Conexão Bar Clip system was also longer than that of the Sterngold Hader Bar system (Table I). Therefore, the clip of the Conexão Bar Clip system had a larger frictional area. As Botega et al1 stated, the greater the friction, the greater the retention. However, maximum retention strength is measured when these clip retentive parts extend beyond the diameter of the retentive portion of the bar. The smaller the amount of open space between the clip’s retentive parts, the greater the resistance is when passing the retentive area of the bar, thereby increasing retention strength. The distance between the retentive parts of the Conexão Bar Clip system is greater than that of the Sterngold Hader Bar system, while the bars are essentially the same diameter. Moreover, the clip of the Conexão Bar Clip system is manufactured with polytetrafluoroethylene, while the Sterngold Hader Bar clip is manufactured with nylon. The clip of the Conexão Bar Clip system is larger in size, and, therefore, presents a greater frictional area and greater resistance (Table I). However, similar retentive strength was observed between these systems (Table III). A comparison of the metal clip systems, SIN Clipo and 3i Gold Hader Type Clip (Table III), indicates that there was no significant difference between these systems. The difference in thickness of retentive parts of the 3i Gold Hader Type Clip and SIN Clipo is only 0.2 mm. These 2 systems presented identical clip length. Moreover, the alloy used in both systems is similar, according to the manufacturers. Thicker retentive clip parts and reduced space between them will present greater resistance when exceeding the bar diameter. The distance between the retentive clip parts in the 3i Gold Hader Type Clip system was smaller than that in the SIN Clipo system; however, the bar diameter was greater and the retentive clip parts thicker (Table I). These factors may

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August 2009 have been responsible for the higher 3i Gold Hader Type Clip retention strength values, but both systems have the same clip length and are made from the same alloy (Table III). The SIN Clipo system demonstrated a significantly smaller retention strength than the Sterngold Hader Bar and Conexão Bar Clip systems, probably because it had the smallest components. SIN Clipo had the thinnest retentive clip part, the shortest clip, and the smallest bar diameter compared to the Sterngold Hader Bar and Conexão Bar Clip systems (Table I). The retention strength of Sterngold Hader Bar and 3i Gold Hader Type Clip systems was not significantly different (Table III). This was probably due to similarities in the systems’ characteristics. The difference in thickness of the retentive part between Sterngold Hader Bar and 3i Gold Hader Type Clip systems was only 0.1 mm, and the bar diameter was the same for these 2 systems (Table I). Conexão Bar Clip and 3i Gold Hader Type Clip systems were significantly different (Table III). The clip of the Conexão Bar Clip system is much longer compared to that of 3i Gold Hader Type Clip. The Conexão Bar Clip system also has a thicker retentive clip part than the 3i Gold Hader Type Clip. The greater retention strength of the Conexão Bar Clip was probably due to its clip characteristics (Table I). The greater size of the clip in the Conexão Bar Clip system gives it a larger frictional area, which results in greater retention. In evaluating the 3i Gold Hader Type Clip system, a successive though not significant increase in retention strength was observed, with a decrease after 4400 cycles. The SIN Clipo system also presents increasing values, but with a single decrease in retention strength at 2200 cycles (Table III). This dip in retention strength can be explained by the fact that when a material receives tension below its elastic limit, and the tension is re-

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lieved soon after, the material returns to its original form without internal or structural alterations. However, when this tension is applied repeatedly, as characterizes a fatigue process, the material can suffer permanent deformation (abrasion, deformation, deterioration, or internal roughness).2 This concept of fatigue may explain increasing retentive strength values followed by a decrease in values without a significant difference. Under clinical conditions, horizontal and oblique strengths, as well as mastication and other forces, including parafunction, can occur, although they were not simulated in this in vitro study. Therefore, the fatigue test, consisting of insertion and removal of overdenture components along the long axis of the implant, may not be the principal cause of reduced retention strength values, nor would the cycling motion likely be responsible for failure of system components.2 Moreover, intraoral characteristics, such as saliva components and temperature, would also influence results. Despite its limitations, this study provides data to explain the behavior of these systems under the tested conditions. All retention strength values were above the minimum necessary (5 N) described in the literature for prosthesis stability.13 Systems with polymer clips are indicated for implant-retained overdentures19 because they are preferred by patients, due to the greater retentive strength of these systems as compared with others.8 The clip of the Conexão Bar Clip system has a vertical lug that facilitates its attachment within the prosthesis. It is important to note that insertion of the clip in the prosthesis is better achieved in the clinic and not in the laboratory.1 When the clip is attached intraorally, it is not exposed to the same errors to which laboratory casts are subject, such as impression material and plaster distortion. Metal clips present lower retention strength; however, the Conexão Bar Clip system contains clip lugs that join to the acrylic resin

in the interior of the prosthesis base, resulting in sufficient resistance. Although this study helps to explain the behavior of overdenture systems manufactured with different materials by submitting them to fatigue tests, as with any in vitro study, it presents limitations, since clinical conditions are not completely simulated.2,13 Therefore, clinical studies are needed to confirm or refute the results found in this in vitro study.

CONCLUSIONS Within the limitations of this study, the following conclusions were drawn: 1. All systems evaluated demonstrated mean retention above the clinically acceptable level described in the literature of 5 N. 2. Systems generally demonstrated significantly increased retention strength values as the cycle number increased. 3. There was no significant difference in retentive strength between the 2 polymer clip systems, nor between the systems with metal clips.

REFERENCES 1. Botega DM, Mesquita MF, Henriques GE, Vaz LG. Retention force and fatigue strength of overdenture attachment systems. J Oral Rehabil 2004;31:884-9. 2. Walton JN, Ruse ND. In vitro changes in clips and bars used to retain implant overdentures. J Prosthet Dent 1995;74:482-6. 3. Chung KH, Chung CY, Cagna DR, Cronin JR Jr. Retention characteristics of attachment systems for implant overdentures. J Prosthodont 2004;13:221-6. 4. Hug S, Mantokoudis D, Mericske-Stern R. Clinical evaluation of 3 overdenture concepts with tooth roots and implants: 2-year results. Int J Prosthodont 2006;19:236-43. 5. Breeding LC, Dixon DL, Schmitt S. The effect of simulated function on the retention of bar-clip retained removable prostheses. J Prosthet Dent 1996;75:570-3. 6. Naert I, Quirynen M, Hooghe M, van Steenbergue D. A comparative prospective study of splinted and unsplinted Brånemark implants in mandibular overdenture therapy: a preliminary report. J Prosthet Dent 1994;71:486-92. 7. Cohen BI, Pagnillo M, Condos S, Deutsch AS. Comparative study of two precision overdenture attachment designs. J Prosthet Dent 1996;76:145-52.

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Volume 102 Issue 2 8. Cune M, van Kampen F, van der Bilt A, Bosman F. Patient satisfaction and preference with magnet, bar-clip, and ball-socket retained mandibular implant overdentures: a cross-over clinical trial. Int J Prosthodont 2005;18:99-105. 9. Epstein DD, Epstein PL, Cohen BI, Pagnillo MK. Comparison of the retentive properties of six prefabricated post overdenture attachment systems. J Prosthet Dent 1999;82:579-84. 10.Attard NJ, Laporte A, Locker D, Zarb GA. A prospective study on immediate loading of implants with mandibular overdentures: patient-mediated and economic outcomes. Int J Prosthodont 2006;19:67-73. 11.Mensor MC Jr. Attachment fixation for overdentures. Part I. J Prosthet Dent 1977;37:366-73. 12.Burns DR, Unger JW, Elswick RK Jr, Giglio JA. Prospective clinical evaluation of mandibular implant overdentures: Part II--Patient satisfaction and preference. J Prosthet Dent 1995;73:364-9. 13.Besimo CE, Guarneri A. In vitro retention force changes of prefabricated attachments for overdentures. J Oral Rehabil 2003;30:671-8.

14.Setz I, Lee SH, Engel E. Retention of prefabricated attachments for implant stabilized overdentures in the edentulous mandible: an in vitro study. J Prosthet Dent 1998;80:323-9. 15.Petropoulos VC, Smith W. Maximum dislodging forces of implant overdenture stud attachments. Int J Oral Maxillofac Implants 2002;17:526-35. 16.Gamborena JI, Hazelton LR, NaBadalung D, Brudvik J. Retention of ERA direct overdenture attachments before and after fatigue loading. Int J Prosthodont 1997;10:123-30. 17.Williams BH, Ochiai KT, Hojo S, Nishimura R, Caputo AA. Retention of maxillary implant overdenture bars of different designs. J Prosthet Dent 2001;86:603-7. 18.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. Clin Oral Implants Res 2003;14:720-6.

19.Payne AG, Solomons YF. Mandibular implant-supported overdentures: a prospective evaluation of the burden of prosthodontic maintenance with 3 different attachment systems. Int J Prosthodont 2000;13:246-53. 20.Porter JA Jr, Petropoulos VC, Brunski JB. Comparison of load distribution for implant overdenture attachments. Int J Oral Maxillofac Implants 2002;17:651-62. Corresponding author: Dr Monica Nogueira Pigozzo Rua Orlando Matielo, 57 Jaú, São Paulo 17207-750 BRAZIL Fax: +5514 3625 5220 E-mail: [email protected] or mpigozzo@ usp.br Copyright © 2009 by the Editorial Council for The Journal of Prosthetic Dentistry.

Correction The article by Kinsel et al entitled “Retrospective analysis of porcelain failures of metal ceramic crowns and fixed partial dentures supported by 729 implants in 152 patients: Patient-specific and implant-specific predictors of ceramic failure,” published in the June 2009 issue of the Journal (J Prosthet Dent 2009;101:388-394), contained an error. Table IV, referenced on page 392 of the Journal, was omitted from the published article. The omitted table appears below.

Table IV. Odds ratio (OR) estimates (95% confidence interval (CI)) for comparison of opposing dental condition, bruxism, and occlusal device use with respect to ceramic failures

Major Ceramic Failure (n=58) OR (95% CI)

Major and Minor Ceramic Failure (n=94) OR (95% CI)

Opposing dentition MC-Implant vs. Tooth MC-Tooth vs. Tooth

13.95 (2.25, 86.41)* 4.59 (0.77, 24.94)

7.06 (2.57, 19.37)* 1.90 (0.91, 4.52)

Bruxism Yes vs. No

5.60 (1.88, 16.66)*

7.23 (3.86, 13.54)*

1.92 (0.62, 5.99)

1.92 (1.01, 3.67)*

Occlusal device Without vs. With

*Partial proportional odds model using generalized estimating equation (GEE) binomial method with P<.05.

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