Assessment of the Survival of a Single Implant-Supported Cantilever Prosthesis in the Anterior Mandible.

BACKGROUND: Implant dentistry has seen rapid and remarkable progress in recent years. The present study assessed the survival of a single implant-supported cantilever prosthesis (ISCP) in the anterior mandible.
MATERIALS AND METHODS: Sixty-four patients with missing mandibular anterior teeth of both genders were provided with a single implant and restored with cantilever screw-retained prosthesis. All were followed for 2.5 years for the implant and prosthetic success.
RESULTS: Age group of 20-30 years comprised 14 males and 10 females, 30-40 years had 10 males and eight females, 40-50 years had six males and seven females, and 50-60 years had four males and five females. The difference was nonsignificant (P > 0.05). A screw loosening was seen in total of 15 cases, in 1 at 12 months, 5 at 18 months, 2 at 24 months, and 7 at 30 months, and porcelain fracture was seen in total of eight cases, in 4 at 18 months, 1 at 24 months, and 3 at 30 months. The difference was statistically significant (P < 0.05).
CONCLUSION: Screw-retained ISCP developed complications such as screw loosening and porcelain fracture. Copyright:

INTRODUCTION

Implant dentistry has seen rapid and remarkable progress in recent years.[1] Several questions have been raised concerning materials as well as designs of both implants and implant abutments to achieve maximum clinical success rates.[2] One of the debates is the choice between screw- and cement-retained implant prostheses, which has long been discussed, but the best type of implant prosthesis remains controversial among practitioners.[34]

Implant-supported fixed prosthesis (ISP) may be single or multiple implant-supported restorations and also cantilever prosthesis.[5] The appreciably high clinical success rate of single and multiple ISP restored with implant-protected occlusion in situations of adequate bone support has been well known. ISP with cantilever molar extensions is usually unilateral/full mouth restorations in the clinical conditions of resorbed maxillary or mandibular posterior ridges.[67]

The use of implant-supported single crowns has become a well-established and preferred approach to compensate missing single teeth.[8] There are two different types of prosthetic restorations fixed on dental implants: screw-retained and cemented restorations. The choice of method is usually based on the clinician's preference.[910] Retrievability is the main advantage of screw-retained crowns that would make it more favorable to many clinicians. Implant-supported screw-retained cantilever prosthesis in mandibular anterior region, which has been a treatment option for edentulous sites with inadequate mesiodistal space.[11] The present study assessed the survival of a single implant-supported cantilever prosthesis (ISCP) in the anterior mandible.

MATERIALS AND METHODS

The present study comprised 64 patients with missing mandibular anterior teeth of both genders. Those who gave their consent to be the part of the study were included. Ethical clearance for conducting study on patients in the department of prosthodontics, bridge, and crown work was initially obtained.

All enrolled patients had missing mandibular central incisors in the age range of 20–60 years of both genders. A thorough clinical examination was performed. Oral health and hygiene of patients were assessed. A single implant was used to replace the missing teeth and restored with cantilever screw-retained prosthesis. All the steps were performed by single prosthodontics following strict sterilization protocol. All were prescribed chlorhexidine mouth wash 2–3 times daily for 7 days. All were followed for 2.5 years for the implant and prosthetic success. Results thus obtained were subjected to statistical analysis. P < 0.05 was considered statistically significant.

RESULTS

Table 1 and Graph 1 show that age group 20–30 years comprised 14 males and 10 females, 30–40 years had 10 males and eight females, 40–50 years had six males and seven females, and 50–60 years had four males and five females. The difference was nonsignificant (P > 0.05).

Table 1

Age- and gender-wise distribution of patients

Age group (years)	Male	Female	P
20-30	14	10	0.05
30-40	10	8	0.25
40-50	6	7	0.92
50-60	4	5	0.91

Graph 1

Age- and gender-wise distribution of patients

Table 2 and Graph 2 show that screw loosening was seen in total of 15 cases, in 1 at 12 months, 5 at 18 months, 2 at 24 months, and 7 at 30 months, and porcelain fracture was seen in total of 8 cases, in 4 at 18 months, 1 at 24 months, and 3 at 30 months. The difference was significant (P < 0.05).

Table 2

Clinical outcome of implant-supported cantilever prosthesis

Time duration (months)	Screw loosening	Porcelain fracture	P
6	0	0	0.01
12	1	0
18	5	4
24	2	1
30	7	3

Graph 2

Clinical outcome of implant supported cantilever prosthesis

DISCUSSION

The screw-retained restorations where the screw-access hole occupies more than 50% of the intercuspal occlusal table require an occlusal restorative material to cover the screw-access channel; these restorative materials are susceptible for wearing under functional forces and so the occlusal contacts will be less preserved than when using cement-retained restorations with intact occlusal surface.[1213] The factors that are affected by different methods of retention of the prostheses to the implants are ease of fabrication and cost, esthetics, access, occlusion, retention, incidence of loss of retention, retrievability, passivity of fit, restriction of implant position, effect on peri-implant tissue health, provisionalization, immediate loading, impression procedures, porcelain fracture, and clinical performance.[14] The choice of a screw-retained versus a cemented crown is a decision that involves several points of consideration. The clinician should have good awareness regarding the advantages and disadvantages of using a screw-retained versus a cemented crown.[15] The present study assessed the survival of a single ISCP in the anterior mandible.

In the present study, age group of 20–30 years comprised 14 males and 10 females, 30–40 years had 10 males and eight females, 40–50 years had six males and seven females, and 50–60 years had four males and five females. Nelluri et al.[16] conducted a study on 30 patients with missing both mandibular central incisors. A single implant was used to replace the missing teeth and restored with cantilever screw-retained prosthesis. Twenty-two patients were followed for 3 years for the implant and prosthetic success. Survival probability of the ISCP for the first 100 days was found to be 97.55%, for 200 days, it was 71.4%, for 250 days, it was 46%, and for 365 days, it was 3.9%, i.e., 20 prostheses had screw loosening after prosthetic loading. However, it increased to 95.2% at the end of 3 years.

We found that screw loosening was seen in total of 15 cases, in 1 at 12 months, 5 at 18 months, 2 at 24 months, and 7 at 30 months, and porcelain fracture was seen in total of 8 cases, in 4 at 18 months, 1 at 24 months, and 3 at 30 months. Aglietta et al.[17] assessed the survival rates of short-span implant-supported cantilever fixed dental prostheses and concluded that cantilevers showing not much detrimental effects and are a valid treatment modality. Kreissl et al.[18] in their study stated that, at the end of 5 years, a cumulative incidence of screw loosening was 6.7%, screw fracture was 3.9%, and porcelain fractures was 5.7% with single implant crowns. However, the complications with cantilever prosthesis were high, 68.6%.

Screw-retained restorations are associated with screw loosening complication, especially in single crown restoration. The frequency of screw loosening is reported to be between 5% and 65%. Using a mechanical torque instrument to tighten the screw to a recommended torque level (20–30 Ncm) has greatly diminished this prosthetic complication. Pjetursson et al.[19] conducted a systematic review and reported that the survival rate of metal-ceramic implant-supported fixed dental prosthesis was 96.4% after 5 years and 93.9% after 10 years. The most frequent complications over the 5-year observation period were fractures of the veneering material (13.5%), loss of access hole restoration (5.4%), abutment or screw loosening (5.3%), and loss of retention of the cemented prosthesis (4.7%).

Zurdo et al.[20] in a systematic review on the survival and complication rates of implant-supported fixed partial denture with cantilevers concluded that cantilever extension has minor technical complications and stated that limited data were available. However, the study does not specify anterior or posterior cantilevers.

CONCLUSION

Authors found that screw-retained ISCP developed complications such as screw loosening and porcelain fracture.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.