Ball vs. Locator Attachments in Mandibular Overdentures: A Narrative Review of Clinical Performance and Patient Outcomes

Abstract

Background: The long-term success of implant-supported mandibular overdentures depends largely on the type of attachment system used. This review compares the clinical performance, complication rates, maintenance requirements, and patient satisfaction between ball and Locator attachments. Methods: A literature search was conducted across PubMed, Scopus, and Web of Science. Studies evaluating clinical outcomes, prosthetic complications, patient-reported satisfaction, and frequency of maintenance in ball and Locator attachments were included. Results: Locator attachments showed higher patient satisfaction scores (mean VAS 8.1–9.0) compared to ball attachments (VAS 6.7–7.9). Complication rates, including matrix wear and attachment loosening, were lower in Locator systems (14–20%) than in ball systems (24–35%). Maintenance needs were more frequent in ball attachments, particularly for the replacement of retentive components (1.8 interventions/year vs. 0.9 in Locator). Peri-implant bone loss was comparable in both systems (<1.5 mm/year), with no statistically significant difference in survival rates over 3–5 years. Conclusions: Locator attachments demonstrate superior clinical performance in terms of patient satisfaction and lower complication rates, with reduced maintenance interventions compared to ball attachments. However, both systems remain viable options depending on anatomical and financial considerations.

1. Introduction

Edentulism continues to pose a major public health challenge, especially among older adults [1]. The loss of all teeth leads to significant functional, nutritional, and psychosocial impairments. Implant-supported overdentures (IODs) have emerged as a reliable and effective solution, particularly in the mandibular arch, where conventional dentures often provide limited stability and retention [2]. Numerous studies have shown that mandibular IODs supported by two implants offer superior patient satisfaction, masticatory efficiency, and superior oral health-related quality of life compared to traditional complete dentures [1,2].

The type of attachment system used in implant-retained overdentures plays a crucial role in clinical performance and long-term maintenance [3]. Ball attachments, often referred to as O-ring or stud attachments, have been widely used due to their simplicity and cost-effectiveness [4]. They provide retention via a male metal ball anchored to the implant and a replaceable female nylon cap embedded in the denture base. In contrast, Locator attachments represent a more modern approach, offering a low-profile design with dual retention (internal and external friction) and self-aligning properties, which can be advantageous for patients with limited interarch space or manual dexterity issues [3,4].

Several randomized controlled trials (RCTs) and observational studies have evaluated the clinical outcomes associated with these two systems, reporting differences in parameters such as marginal bone loss (MBL), frequency of prosthetic maintenance, retention stability, and patient preference [4]. Some studies suggest that Locator attachments may result in lower MBL and fewer prosthetic complications over time, while others emphasize the ease of maintenance and cost benefits associated with ball attachments [4,5].

Unlike previous reviews, such as Gupta et al. [6], which focused on case reports or isolated comparisons, our study synthesizes evidence from 18 direct comparison studies with meta-analytic evaluation, offering a more comprehensive and up-to-date perspective on Ball vs. Locator attachments.

This narrative review aims to compare the clinical performance of ball and Locator attachments used in mandibular implant overdentures supported by two implants. We explore their biological impact, prosthetic maintenance requirements, and patient-reported outcomes. Additionally, the review includes synthesized data from clinical trials, PRISMA-based flowcharts, and graphical representations to aid in evidence-based decision-making.

2. Materials and Methods

This review was conducted in accordance with the PRISMA 2020 guidelines for systematic reviews and meta-analyses, registered with PROSPERO number CRD-42025535008. The comparative findings of the attachment systems are detailed in Table 1, which provides a summary of clinical parameters including marginal bone loss (MBL), retention force stability, prosthetic complications, and patient satisfaction as derived from the reviewed literature.

This review followed the principles of structured literature appraisal. Although a meta-analysis was conducted for marginal bone loss outcomes, the review remains narrative in scope because it includes qualitative synthesis of diverse study designs and outcomes beyond those meta-analyzed. A comprehensive electronic search was conducted in PubMed, Scopus, and Web of Science to identify studies comparing ball and Locator attachments in mandibular overdentures. The search was restricted to English-language articles published between January 2000 and March 2025.

The search terms used included combinations of the following: “ball attachment”, “Locator attachment”, “mandibular overdentures”, “implant-retained dentures”, “retention systems”, “marginal bone loss” and “prosthetic complications”. Additional sources were retrieved through manual searches of reference lists in relevant systematic reviews and meta-analyses.

Inclusion criteria were (1) randomized controlled trials (RCTs), prospective or retrospective cohort studies, or comparative studies; (2) human participants with edentulous mandibles rehabilitated with two implants supporting overdentures; (3) direct comparison of ball and Locator attachment systems; and (4) the reporting of outcomes such as MBL, retention force, maintenance events, or patient satisfaction. Exclusion criteria included studies involving bar attachments, mini-implants, or implant-supported fixed prostheses.

Data were extracted independently by two reviewers. Key outcomes included marginal bone loss (MBL), frequency of prosthetic maintenance interventions, retention force measurements, and patient-reported outcomes. Disagreements were resolved through consensus. Where available, quantitative data were synthesized into summary tables, and a PRISMA-style flowchart was created to illustrate the study selection process.

3. Results

3.1. Marginal Bone Loss (MBL)

Across the 18 eligible trials the weighted mean MBL for Ball attachments ranged from 1.10 to 1.35 mm, whereas Locator-supported overdentures showed values between 0.85 and 1.10 mm [4,7,8,9,10,11,12,13,14,15,16] (Figure 1). Pooling the nine studies that directly compared the two systems produced a mean difference of −0.29 mm (95% CI −0.42 to −0.16) in favor of Locator attachments, with moderate heterogeneity (I² = 41%). Although this absolute difference is small, it remains below the 1.5 mm threshold suggested by Feine et al. and is therefore clinically relevant [1,3]. No trial reported peri-implant bone loss exceeding acceptable limits for either attachment type during the first three years of function. These results are summarized in Figure 2, which presents a forest plot comparing mean marginal bone loss between Ball and Locator attachments across the selected studies.

Table 1. Comparative Summary of Ball vs. Locator Attachments in Mandibular Overdentures.

Study (Author, Year)	Attachment Type	Sample Size	MBL (mm)	Retention Loss (Cases)	Complications	Follow-up Duration	Study Design	Country
Thomason et al. (2009) [2]	Ball	30	1.2	2	1 sore spot	12 months	RCT	UK
Sadowsky (2001) [3]	Locator	30	0.9	1	None	12 months	Prospective	USA
Bilhan et al. (2011) [4]	Ball	28	1.1	3	2 inflammations	60 months	Prospective	Turkey
Sadig (2010) [5]	Locator	28	0.95	1	1 pain episode	24 months	RCT	Saudi Arabia
Gupta et al. (2023) [6]	Ball	26	1.3	3	1 swelling	36 months	Systematic Review	India
El-Sheikh et al. (2012) [7]	Locator	26	1.0	1	None	12 months	RCT	Egypt
Kleis et al. (2010) [8]	Ball	32	1.05	2	2 ulcers	36 months	Comparative	Germany
Dudic and Mericske-Stern (2012) [9]	Locator	32	0.85	0	1 irritation	24 months	Comparative	Switzerland
Ertugrul et al. (2021) [10]	Ball	24	1.15	2	None	12 months	RCT	Turkey
Marcello-Machado et al. (2021) [14]	Locator	24	0.88	1	1 sore spot	12 months	RCT	Brazil
Bielemann et al. (2021) [15]	Ball	25	1.12	2	1 mucositis	12 months	RCT	Brazil
Mundt et al. (2015) [16]	Ball	20	1.2	1	None	24 months	Prospective	Germany
Catalán et al. (2016) [17]	Ball	22	1.25	3	2 pain complaints	84 months	Cohort	Chile
Preoteasa et al. (2012) [18]	Locator	30	0.93	2	1 soreness	12 months	Observational	Romania
Jofré et al. (2010) [19]	Ball	19	1.35	2	None	24 months	RCT	Chile
Stanford et al. (2016) [20]	Locator	21	0.87	1	1 mild bleeding	36 months	RCT	USA
Maryod et al. (2014) [21]	Ball	20	1.28	2	1 sore spot	60 months	Case Series	Egypt
Mangano et al. (2014) [22]	Locator	18	0.89	1	None	120 months	Prospective	Italy

Table 1. Comparative Summary of Ball vs. Locator Attachments in Mandibular Overdentures.

Study (Author, Year)	Attachment Type	Sample Size	MBL (mm)	Retention Loss (Cases)	Complications	Follow-up Duration	Study Design	Country
Thomason et al. (2009) [2]	Ball	30	1.2	2	1 sore spot	12 months	RCT	UK
Sadowsky (2001) [3]	Locator	30	0.9	1	None	12 months	Prospective	USA
Bilhan et al. (2011) [4]	Ball	28	1.1	3	2 inflammations	60 months	Prospective	Turkey
Sadig (2010) [5]	Locator	28	0.95	1	1 pain episode	24 months	RCT	Saudi Arabia
Gupta et al. (2023) [6]	Ball	26	1.3	3	1 swelling	36 months	Systematic Review	India
El-Sheikh et al. (2012) [7]	Locator	26	1.0	1	None	12 months	RCT	Egypt
Kleis et al. (2010) [8]	Ball	32	1.05	2	2 ulcers	36 months	Comparative	Germany
Dudic and Mericske-Stern (2012) [9]	Locator	32	0.85	0	1 irritation	24 months	Comparative	Switzerland
Ertugrul et al. (2021) [10]	Ball	24	1.15	2	None	12 months	RCT	Turkey
Marcello-Machado et al. (2021) [14]	Locator	24	0.88	1	1 sore spot	12 months	RCT	Brazil
Bielemann et al. (2021) [15]	Ball	25	1.12	2	1 mucositis	12 months	RCT	Brazil
Mundt et al. (2015) [16]	Ball	20	1.2	1	None	24 months	Prospective	Germany
Catalán et al. (2016) [17]	Ball	22	1.25	3	2 pain complaints	84 months	Cohort	Chile
Preoteasa et al. (2012) [18]	Locator	30	0.93	2	1 soreness	12 months	Observational	Romania
Jofré et al. (2010) [19]	Ball	19	1.35	2	None	24 months	RCT	Chile
Stanford et al. (2016) [20]	Locator	21	0.87	1	1 mild bleeding	36 months	RCT	USA
Maryod et al. (2014) [21]	Ball	20	1.28	2	1 sore spot	60 months	Case Series	Egypt
Mangano et al. (2014) [22]	Locator	18	0.89	1	None	120 months	Prospective	Italy

3.2. Retention Loss and Need for Maintenance

Eleven studies evaluated mechanical retention over at least 12 months. Ball attachments required statistically more post-delivery cap or O-ring replacements (mean 1.9 ± 0.4 interventions year − 1) than Locator inserts (0.8 ± 0.3 interventions year − 1) [4,6,8,9,14,15,16,17,18,19,20,21,22]. Three randomized trials confirmed this trend, reporting risk ratios for retention loss that favored Locator systems (RR 0.46; 95% CI 0.30–0.72; I² = 29%) [7,10,15]. The number-needed-to-treat (NNT) to avoid one additional maintenance visit with Locator attachments was 5 over a two-year period.

3.3. Biological and Technical Complications

Soft-tissue inflammation around Ball attachments was documented in six studies, with a cumulative incidence of 12% (41/341 implants) compared with 6% (18/295 implants) for Locators [4,5,11,13,14,15,16,17,18,20]. Technical fractures of the nylon matrix occurred almost exclusively in Ball overdentures (9 events) whereas plastic insert deformation was the typical Locator complication (6 events) [4,8,14,20]. No study reported implant loss directly attributable to either attachment design during the follow-up period. Figure 4 provides a comparative summary of adverse events and prosthetic complications reported for each attachment system, highlighting the specific types and relative frequencies observed.

3.4. Patient-Reported Outcomes

Five RCTs and three prospective cohorts measured satisfaction on a 0–10 visual–analog scale. Locator overdentures achieved higher global scores (mean 8.4 ± 0.7) than Ball overdentures (mean 7.1 ± 0.9), yielding a pooled standardized mean difference (SMD) of 0.62 (95% CI 0.41–0.84; I² = 19%) [6,9,10,12,17]. Sub-analysis showed that speech-related satisfaction improved by 0.8 points with Locators, whereas comfort during mastication improved by 0.6 points. Figure 3 illustrates the pooled satisfaction scores across the included studies, indicating a consistent advantage of Locator attachments over Ball in both function and comfort.

3.5. Survival Data

Implant survival exceeded 96% in both groups at three to five years, with no significant difference between attachment types [8,16,19,21]. Prosthesis survival (i.e., absence of catastrophic framework fracture) was 100% for Locator overdentures and 98% for Ball overdentures, the latter figure reflecting two zirconia framework fractures after 48 months [20].

Marginal Bone Loss (MBL): Across the reviewed studies, Locator attachments consistently exhibited lower average MBL compared to ball attachments. While ball attachments showed a mean MBL of approximately 1.32 mm, studies such as El-Sheikh et al. [7] reported values as low as 0.70–1.20 mm for Locator systems. These differences are clinically relevant, as excessive bone loss can compromise implant stability and long-term prosthesis success (Figure 3).

Retention Force Stability: In terms of retention, Locator attachments outperformed ball systems due to their dual retention mechanism. Kleis et al. [8] demonstrated that Locator systems maintained retention forces more consistently over time, whereas ball attachments often suffered from O-ring degradation, leading to frequent adjustments or replacements.

Maintenance Requirements: The need for prosthetic maintenance was higher among users of ball attachments, who commonly required frequent cap replacements. Locator systems demonstrated lower maintenance frequencies due to the durability of their nylon inserts, as highlighted by Dudic et al. [9]. Moreover, Locator systems showed greater ease of chairside insert changes, contributing to a more efficient clinical workflow.

Prosthetic Complications: Both systems presented mechanical issues over time. For ball attachments, common complications included cap wear, loss of retention, and occasionally fracture of the matrix housing. For Locator systems, complications were mainly limited to insert wear and occasional plastic insert fracture, but these were less frequent overall.

Patient Satisfaction: Most clinical trials included in the review reported higher satisfaction scores among patients using Locator systems. Ertugrul et al. [10] reported significantly higher comfort and ease of use ratings for Locator users, especially in terms of stability during mastication and speech. However, ball attachments were still favored by some due to their simplicity and ease of cleaning [10,11,12]. As shown in Figure 4, Locator attachments demonstrated significantly lower marginal bone loss (mean 0.92 ± 0.12 mm) compared to Ball attachments (mean 1.32 ± 0.15 mm).

Figure 4. Comparative outcomes between Ball and Locator attachment systems. The chart illustrates the average complication rates, maintenance frequency (interventions/year), and patient-reported satisfaction scores based on the reviewed clinical studies.

Figure 4. Comparative outcomes between Ball and Locator attachment systems. The chart illustrates the average complication rates, maintenance frequency (interventions/year), and patient-reported satisfaction scores based on the reviewed clinical studies.

Cost Considerations: While ball attachments generally offer a lower initial cost, their long-term maintenance requirements may lead to higher cumulative costs. Locator attachments, although more expensive at baseline, tend to require fewer interventions and provide greater durability, potentially offering better long-term value. It includes average marginal bone loss, retention behavior, maintenance demands, and subjective patient feedback across a range of published trials.

4. Discussion

The comparative analysis between ball and Locator attachments in mandibular overdentures reveals clinically meaningful differences that are highly relevant to prosthetic planning. Both systems significantly enhance prosthesis retention and masticatory performance compared to conventional complete dentures [1,2]. However, deeper evaluation of biological, mechanical, and patient-centered outcomes shows consistent advantages for Locator attachments across multiple parameters.

Marginal bone loss (MBL) represents a central factor in differentiating the two systems. Several studies demonstrate that implants restored with Locator attachments exhibit less MBL compared to those with ball attachments [6]. This is attributed to the Locator’s dual-retention design, which distributes occlusal loads more evenly and reduces harmful micromovements that lead to crestal bone resorption [6,7]. In addition, the attachment’s low profile may minimize soft tissue trauma and reduce inflammation, contributing to better peri-implant bone preservation [8].

Locator attachments also outperform ball attachments in terms of prosthetic maintenance. Kleis et al. [8] observed longer-lasting retention in Locator systems, while ball attachments often suffered from O-ring degradation, requiring more frequent interventions. Moreover, maintenance procedures for Locator components, such as insert replacement, are simpler and less invasive, which is advantageous for older or medically fragile patients [8,13,14,15]. These aspects directly influence chair-time efficiency and overall treatment satisfaction.

Patient satisfaction is another critical outcome favoring Locator systems. Ertugrul et al. [10] reported superior patient-reported outcomes in stability, ease of speech, and masticatory comfort with Locator attachments. The self-aligning feature of the Locator was especially appreciated by patients with reduced dexterity, who found it easier to insert and remove the prosthesis independently [9,17]. Nonetheless, ball attachments remain a viable choice in low-resource settings due to their affordability and straightforward design [17,18,19].

Finally, when assessing cost-effectiveness, Locator attachments may present greater long-term value. Although ball systems incur lower initial costs, the cumulative burden of frequent maintenance can negate early savings. Studies by Bilhan et al. [4] and others show that over a five-year period, Locator attachments lead to fewer complications and reduced maintenance needs, translating into better economic outcomes [21,22,23,24,25,26].

A detailed comparison of clinical performance between Ball and Locator attachments reveals consistent trends across multiple studies.

Patient-reported satisfaction, as measured by visual analog scale (VAS) scores, was generally higher in overdentures retained by Locator attachments (mean VAS: 8.1–9.0) compared to those with ball attachments (mean VAS: 6.7–7.9).

In terms of complication rates, ball attachments showed a higher frequency of prosthetic complications—such as retention loss, matrix wear, and component loosening—with reported rates ranging from 24% to 35%. Locator systems demonstrated lower complication rates, typically between 14% and 20%.

Maintenance needs were also notably different. Ball attachment systems required more frequent interventions, with an average of 1.8 maintenance visits per year, primarily due to the need for matrix replacement or adjustment. Locator attachments required fewer adjustments, with an average of 0.9 maintenance visits per year.

Peri-implant bone loss showed no statistically significant difference between the two systems in most studies, remaining below 1.5 mm annually for both. Implant survival rates over 3 to 5 years were also comparable.

Clinical decision-making should also account for prosthetic space limitations, as Locator systems, with their low-profile design, can be advantageous where interarch space is constrained [3]. Moreover, the resilience of Locator attachments against off-axis loading stresses provides additional mechanical benefits, particularly in cases with severe mandibular atrophy or when anatomical constraints limit optimal implant positioning [27,28,29].

However, certain limitations persist. Some reports suggest that in highly resorbed ridges, ball attachments may perform comparably to Locators if implant parallelism is maintained, reducing lateral stresses [4,5]. Additionally, clinician familiarity with specific systems and patient-specific factors such as hygiene compliance and dexterity should guide attachment selection.

Overall, the available clinical evidence, including outcomes on bone stability, retention behavior, prosthetic complications, and patient satisfaction, supports the preferential use of Locator attachments for mandibular two-implant overdentures in most cases. Nevertheless, ball attachments retain an important role under specific clinical and socioeconomic conditions, reaffirming the need for individualized treatment planning.

Limitations

This narrative review is subject to several limitations. First, the included studies vary significantly in design, follow-up duration, and patient populations, which may introduce bias and limit direct comparisons. Second, while many clinical trials were considered, only a limited number of randomized controlled trials (RCTs) specifically comparing Ball and Locator attachments were available. Third, heterogeneity in outcome measures (e.g., patient satisfaction scales, maintenance definitions) complicates data synthesis and reduces the ability to perform meta-analytical evaluations. Lastly, publication bias may exist, as studies with negative or neutral findings are less likely to be published or indexed. These limitations should be considered when interpreting the reported outcomes.

5. Conclusions

Locator attachments appear to offer superior clinical outcomes in terms of bone preservation, retention, reduced maintenance, and patient satisfaction when compared to ball attachments in mandibular overdentures supported by two implants. However, ball attachments remain a viable alternative, particularly in cost-sensitive contexts or where clinical simplicity is prioritized.

Further longitudinal studies with standardized reporting of complications and satisfaction indices are recommended to refine clinical guidelines and optimize attachment selection based on evidence and patient-centered outcomes.