Implant-Supported Overdenture with a Custom Cad/Cam-Fabricated Bar Attachment in Combination with Antirotational Locator® Attachments in a Severely Atrophied Mandible: A Case Report
Anna Winter1*, Soo-Ji Kim2, Janka Kochel3, Juliana Mielke2 and Silvia Brandt2
1Department of Prosthodontics, Dental Clinic of the Medical Faculty, University of Wuerzburg, Germany
2Department of Prosthodontics, Hospital for Dental, Oral and Orthodontic Medicine (Carolinum), Johann Wolfgang Goethe University, Frankfurt am Main, Germany
3Department of Orthodontics, Dental Clinic of the Medical Faculty, University of Wuerzburg, Germany.
*Corresponding author: Anna Winter, University of Wuerzburg, Pleicherwall, Wuerzburg, Tel: +0049 931 201 74707; Fax: 0049 931 201 73221; E-Mail: firstname.lastname@example.org
Citation: Winter A, Kim S-J, Kochel J, Mielke J, Brandt S (2019) Implant-Supported Overdenture with a Custom Cad/Cam-Fabricated Bar Attachment in Combination with Antirotational Locator® Attachments in a Severely Atrophied Mandible: A Case Report. J Clinical Case Rep Case Stud 2019: 31-36.
Received: 02 August, 2019; Accepted: 05 August, 2019; Published: 30 September, 2019
Background: An atrophied mandible, inserting two implants in the edentulous mandible is an established way to improve prosthesis stability. Multiple options for subsequent retention of the denture are available.
Methods: For oral rehabilitation, a modified bar supplemented by antirotational Locator® was used for prosthesis anchoring. This solution ensured and improved retention, despite of the reduced bone supply associated with severe infraposition of the floor of the mouth and limited vertical space.
Results: The surgical and prosthetic procedures provided high denture stability and good chewing ability
Conclusion: It can be concluded that the technique described allows good clinical outcome with minimal complications. It can be recommended to restore edentulous and atrophied mandible.
Keywords: Atrophied mandible, bar attachment, dental implant, edentulous jaw, Locator® attachment, overdenture
The edentulous mandible can present a major challenge to the dental practitioner, as denture retention and fit are often hampered by atrophy of the alveolar crest. It’s often associated with reduced chewing and speech comfort. This can be related to a negative impact on the oral health-related quality of life (OHRQoL) [1,2]. To ensure good denture retention despite the pronounced bone degradation, implants are often inserted to increase the number of available abutments. A removable denture supported by two implants significantly improves the patient’s masticatory function and OHRQoL. This type of rehabilitation is supported by scientific evidence in situations where an overdenture or complete denture is present in the maxilla [3-6].
Various concepts are available for anchoring implant-supported dentures. They can be retained by magnets or ball attachments, but also by telescopic crowns if sufficient vertical space is available [7-10]. In addition, Locator® attachments permit the restoration to be supported by implants . However, care must be taken to ensure that the denture base is appropriately designed. According to Yoo et al., a greater extension of the denture base can have positive influence on the load the implants are subjected to . Another denture anchoring can be realized by the use of a connecting bar, which also achieves good retention and patient satisfaction and can be used in situations with reduced vertical space [13-15].
Consequently, several options are available for the rehabilitation of an edentulous mandible in which two implants have been inserted as abutments. Each of these options has its advantages and disadvantages, which must be carefully considered in the light of the prevailing clinical situation. The presented modified bar-supported prosthetic restoration with antirotational Locator® attachments combines the advantages of both attachment systems. This allows the treatment of severe atrophied alveolar ridges, minimal vertical space and a severely depressed floor of the mouth. Comprehensive or similar cases are missing; thus, this case report allows the presentation of an innovative treatment process.
Diagnosis and treatment planning
A 71-year-old female patient presented with a mandibular complete denture and a sufficient maxillary denture supported by telescope crowns. The lower prosthesis was poorly fitting. The available intermaxillary space was reduced which was not sufficient for a double-crowned prosthesis.
Owing to her severely atrophied alveolar ridge, the patient’s request for better retention of her mandibular denture could be accommodated only by placing implants to increase the number of abutments. However, implant insertion was made difficult by her very limited bone supply, her lingually tilted alveolar ridge, and her severely depressed floor of the mouth (Figure 1). After extensive evaluation and consultation, the insertion of a maximum of two implants was deemed to be possible despite the unfavorable bone situation.
Figure 1: Pre-surgical X ray of atrophied and edentulous mandible
When planning of the superstructure, the extent of the floor of the mouth and the limited vertical space had to be considered in addition to the possible number and angulation of the implants. In addition, the severe infraposition of the floor of the mouth and vestibule further restricted the choice of available superstructure designs. Given the limited contact surface and equally limited tissue surface of the prosthesis, even installing Locator® attachments did not guarantee secure retention. Given this clinical situation, an implant-supported bar was chosen for anchoring the denture. In addition, due to the small footprint of the denture base and the limited possible height of the bar, rotation protection was to be provided by Locator® attachments. Although the existing bar already allowed secure seating of the denture despite the limited available space, the Locator® inserts offered extra retention in addition to their antirotational function.
Two implants were inserted at sites 33 and 43 (Ankylos®, length 6.6 mm; Dentsply Implants, Mannheim, Germany). Following a phase of 3 months submerged healing, the implant sites were surgically exposed. To meet the challenge of the depressed floor of the mouth, a free mucosal graft was placed to improve the gingival situation in the denture-supporting area between sites 33 and 43. Nevertheless the denture bearing surface and the width of attached gingiva was reduced (Figure 2).
Figure 2: Status after reentry and a free mucosal graft. The gingiva formers are in situ. The mandible exhibits severe atrophy and a depressed floor of the mouth.
An open impression of the implants was taken (Impregum Penta®; 3M Espe, Seefeld, Germany). The horizontal and vertical interarch relations as well as esthetic parameters were provisionally defined and an arbitrary maxillary facebow transfer performed (Figure 3).
Figure 3: A jaw relation record is taken using a registration template, aluminum wax and Temp Bond; in the anterior region, Pro Temp is used for the bite registration.
The casts were mounted in an articulator; a wax-up was created and tested at an esthetic try-in. In order to obtain the desired occlusion, the existing implant angulation had to be compensated. This was achieved with angled Balance Base abutments (Ankylos® SmartFix™ concept; Dentsply Implants). PEEK insertion aids allowed to parallelize the abutments, which were then definitely connected (Figure 4).
Figure 4: Intraorally inserted balance abutment at site 43 with an orientation aid for parallel alignment. Note the lingual “opening” for the wrench.
The abutment heads for angled Balanced Base abutments were then inserted. They are located at the end of the insertion aid and can get screwed in place by loosening the insertion aids and turning them by 180° (Figures 5 and 6).
Figure 5: Placement aids for bath sites for placement of the abutment heads for the Balance Base abutment C/ angled.
Figure 6: Balance abutments in place at sites 33 and 43.
A new impression at the abutment level was required for an optimal transfer of the exact intraoral position’s situations of the abutments. For this purpose, congruent retention caps for the pick-up impression (Ankylos® Retention Caps; Dentsply Implants) were connected to the abutments with a long screw. Previously, they had been individualized with pattern resin. In order to ensure an optimized relative alignment of the abutments, the existing pattern-resin templates were splinted intraorally using more pattern resin, and an overimpression (fixation impression) was taken (Figures 7 and 8). Balanced Base abutments were than sealed with sealing caps (Ankylos® Protective Cap for Balance Base abutments; Dentsply Implants). A new jaw relation record was taken and a new wax try-in was performed. Having examined the relevant functional and esthetic parameters, a custom bar was designed and milled using CAD/CAM technology. The wax-up informed the next design step (Figures 9 and 10) following the principle of backward planning. The design included the attachments for the antirotational Locator® attachments at sites 44 and 34 (Figure 10). These Locator® inserts were also integrated into the bar connectors on the basal surface of the denture.
Figure 7: Extraoral view of the retention copings, customized with pattern resin for taking an abutment-level impression.
Figure 8: Retention copings for impression-taking screwed in placed and splinted intraorally using pattern resin.
Figure 9: CAD/CAM fabrication of the bar, digitally designed based on the wax-up.
Figure 10: The completed milled bar with Locator® abutments at sites 34 and 44.
The bar had been tried in before the denture was fabricated and delivered. For the final delivery, the bar was connected with a retaining screw (Ankylos® Fixation Screw Occlusal, M 1.6 mm Hex short, anodized blue; Dentsply Implants) (Figures 11 and 12). After the correct retention adjustment of the Locator® inserts the patient received oral-hygiene instructions. She has been scheduled for semi-annual recall appointments to control and support her oral hygiene. The prosthesis shows a good and stable retention as well as high chewing and wearing comfort during the observation period of almost 2 years. In addition, the patients’ oral health related quality of life improved by the described oral rehabilitation.
Figure 11: Intraorally screw-retained bar with antirotational Locator® abutments at sites 34 and 44.
Figure 12: The definitive restoration in situ.
The chosen approach involves a great deal of effort on both the dentist’s and the dental technician’s side. The treatment period is longer than with other attachment systems, and the increased effort is associated with higher cost. However, the meticulous production process has resulted in a dental prosthesis with a very good and secure fit, stable and secure retention, and good chewing and speech comfort.
This was also the conclusion reached by MacEntee et al., who reported improvements in chewing comfort and speech ability with bar-retained dentures, something that is also reflected by the significantly higher quality of life found by Sánchez-Siles et al. and Awad et al. compared to conventional dentures [15-17]. Mericske-Stern et al.  also demonstrated the good retention, high stability and favorable masticatory function of bar-retained prostheses. In addition, a bar design was preferred in a cross-over comparison with other types of attachment studied by Cune et al. .
However, Naert et al.  reported an increase in the incidence of peri-implant irritation and gingival hyperplasia with bar-retained dentures, which they blamed on the frequently criticized difficulty to ensure adequate bar hygiene. This can be averted by regular oral hygiene instructions and supportive prophylaxis . This agrees well with the findings for the patient presented here, where regular follow-up appointments ensured that the gingiva remained largely free of inflammation. In addition, no repair of the bar-supported denture became necessary during the observation period. This agrees with the results of a study by MacEntee et al. , who reported that bar-retained prostheses needed very little maintenance or repairs.
In the above-mentioned literature, additional attachments were often used to compensate for rotational forces around the bar. Hereby, also an adequate retention and guiding surface of the bar can compensate these rotational forces. In the case under consideration, the height of the bar and therefore its retention surface were limited due to the limited intermaxillary distance. Furthermore, the severely depressed floor of the mouth additionally imperiled the support and stability of the denture. Thus, the bar design selected here was supplemented by Locator® attachments, which added antirotational features and provided additional support and retention despite the difficult intraoral situation. Unlike strictly bar-supported prostheses, a quick and cost-effective improvement of the retention in the event of a loss of retention can be achieved by replacing the Locator® inserts used. This restores the stability of the rehabilitation over the long term and contributes to its favorable prognosis .
Despite increased clinical and laboratory time and effort, the procedure described here can be recommended for the restoration of the edentulous mandible. The use of antirotational Locator® attachments further improves the retention in conditions of limited vertical and basal space.
The authors report no conflicts of interest related to this study.
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