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Year : 2015  |  Volume : 5  |  Issue : 1  |  Page : 6-11

Effect of implant location on palateless complete overdenture retention: Preliminary study

1 Department of Prosthodontics, Faculty of Dentistry, Mansoura University, Mansoura, Egypt
2 Department of Oral Medicine, Faculty of Dentistry, Mansoura University, Mansoura, Egypt

Date of Web Publication2-Apr-2015

Correspondence Address:
Nesma Mohammed El-Amier
# F107 Mazyad Complex House, Mohammed Bin Zayed City, Abu Dhabi, UAE

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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0974-6781.154418

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Aim : To evaluate the influence of implant location on initial retention of palateless complete overdentures retained by four O-rings at different inter-implant distances.
Materials and Methods: Totally, 36 completely edentulous participants were equally assigned into two groups (G1 and G2). G1 participants have received four implants, two in the canine region with 32 mm inter-implant distance, and two in the second premolar region away from the anterior canine implants by 14 mm on both sides. G2 participants have received four implants, two in the canine region with 32 mm inter-implant distance, and two in first molar region away from anterior canine implants by 22 mm on both sides. Both groups have received palateless complete implant overdentures retained by four O-rings. Initial axial and para-axial retention of overdentures of both groups was estimated using digital forcemeter, and compared using an independent t-test.
Results: Independent t-test revealed that location of dental implants has a significant role in the palateless complete overdenture retention with a level of significance set at P < 0.05.
Conclusion: For palateless complete implant overdentures retained by four O-rings, increasing the inter-implant distance between anterior and posterior implants provides a more retentive prosthesis.

Keywords: Dental implants, maxillary, overdenture, retention

How to cite this article:
El-Amier NM, Elsaih EA, El-Motaiam HA, Al-Shahat MA. Effect of implant location on palateless complete overdenture retention: Preliminary study. J Dent Implant 2015;5:6-11

How to cite this URL:
El-Amier NM, Elsaih EA, El-Motaiam HA, Al-Shahat MA. Effect of implant location on palateless complete overdenture retention: Preliminary study. J Dent Implant [serial online] 2015 [cited 2022 May 26];5:6-11. Available from:

   Introduction Top

The patient needs and desires may require the natural palate of the patient to be uncovered while wearing the maxillary denture. These patients include gaggers, patients with large maxillary tori or bony exostoses, singers and actors due to voice changes caused by any change in the prosthesis volume, food and wine consumers who use their palates to taste subtle differences in preparations, and new denture wearers unfamiliar with the palatal aspect of the maxillary denture. [1]

Omission of palatal aspect of the maxillary denture adversely affects its retention, so implants were installed to maintain retention, support, and stability. [2],[3],[4] Several studies have recommended a minimum of four implants to be installed in maxilla while removing partially the palatal coverage. [4],[5],[6],[7],[8]

Anteriorly, canine area is a key implant position while posterior key implant position is still controversial. First molar area may be a key implant position since the bite force doubles in a molar area when compared to the premolar area. [9] In addition, first molar area shows moderate resorption rates while premolar area shows high resorption rates. [10] However, second premolar area may be preferred to avoid maxillary sinus and consequently the need for extensive grafting and sinus lifting procedures. [1],[11]

Although different designs of overdenture attachments have been the scope of many investigations, [12],[13],[14] the potential influence of implant location on prosthesis retention has seldom been investigated. Since, retention has a direct relationship with patient satisfaction; [15] the goal of this study was to determine the influence of implant location on retention of palateless complete overdentures retained by four implants.

   Materials and methods Top

Pilot study for implant site determination

A pilot study was established to determine the inter-canine, canine-second premolar, and canine-first molar distances following the principles applied by Michelinakis et al.[16] One hundred maxillary complete dentures were surveyed in try in stage. The inter-canine distance was measured between the two canine cusp tips, the canine-second premolar distance was measured from the midpoint of second premolar central groove to the ipsi-lateral canine cusp tip, and the canine-first molar distance was measured from the first molar central fossa to the ipsi-lateral canine cusp tip. The three distances were measured in a straight line using digital Boley Gauge (Digital Caliper, IOS, USA). Distances were measured in fractions of millimeters, and the final mean value of each distance was rounded to the nearest millimeter. The clinical mean values of inter-canine, canine-second premolar, and canine-first molar distances were 32, 14 and 22 mm respectively.

Selection of participants

This study was conducted on 36 participants from July 2011 to February 2014 after approval of the local committee for scientific research ethics. Treatment plan was briefly discussed with each participant, before reading and signing formal consents. Participants were completely edentulous with complaints from the complete palatal coverage of their previous dentures. Selected participants had moderately developed alveolar ridges covered with healthy mucosa, square shaped maxillary arches, moderate depth palatal vaults, sufficient inter-arch spaces verified by tentative jaw relations, Angle's class I maxillo-mandibular relationships, and sufficient bone volume to receive maxillary dental implants. Participants were selected free from medical conditions that contraindicate surgical procedures, or adversely affect osseo-integration. Participants with marked undercuts, bony exostoses, severe ridge resorptions, shallow or deep palatal vaults, neuromuscular disorders (e.g.,  Parkinsonism More Details), para-functional habits, or bad habits such as excessive smoking and alcoholism were excluded.

Construction of radiographic and surgical stents

Six marks on the study cast of each participant were made using the digital Boley Gauge so that inter-canine, canine-second premolar, and canine-first molar distances were 32, 14 and 22 mm respectively. Radiographic balls (Friadent® , Ø 5 mm, Mannhelm, Germany) were fixed over marks and a transparent radiographic stent was constructed. Panoramic radiographs were made with stents intraoral then traced by a computer program (CorelDraw X5, ©2010 Corel Corporation) to estimate available bone height opposite to each ball [Figure 1]. According to bone availability, participants were grouped whether to receive their posterior implant in the second premolar region (G1), or in first molar region (G2). Radiographic balls at target implant sites were removed, and their places were drilled into holes to convert the radiographic stent to a surgical stent.
Figure 1: Traced panoramic radiograph with stent intraoral

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Grouping of participants

In group one (G1), 18 participants have received four implants, two implants in canine region with 32 mm inter-implant distance, and two implants in second premolar region away from the anterior canine implants by 14 mm on both sides. In group two (G2), 18 participants have received four implants, two implants in canine region with 32 mm inter-implant distance, and two implants in first molar region away from the anterior canine implants by 22 mm on both sides. All implants were single piece ball type (Slim Line, Dentium Ltd., Co., Korea), with S.L.A surface, Ø 3.5 mm, 12 mm length in canine region, and 10 mm length in second premolar/first molar region [Figure 2].
Figure 2: Four ball type single piece implants installed in maxilla

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Implant installation

Tissue punch (Ø 3 mm) was used to make gingival access at the center of surgical stent holes. Drilling of implant site was performed using the successive drills of Slim Line implant surgical kit (Slim Line, Dentium Ltd., Co., Korea) with final drill diameter of 3.4 mm. Implants were self-tapped manually, and the final seating was performed with a hand ratchet wrench at 35 N. Progressive loading protocol was followed the same as recommended by Lerner, [17] the intaglio surface of patients' previous dentures was relieved opposite to implant balls followed by relining the dentures with cold curing silicone-based soft liner (Promedica, Neumünster, Germany). Participants were instructed to consume soft food for the next 3 months, and were scheduled for monthly recall visits to check oral hygiene and to replace soft liner when necessary. After 3 months, stability of implants was assessed by Periotest (Periotest S, Medizintechnik Gulden e.K., Germany). Periotest values ranged from −8 to 0 have indicated adequate osseo-integration.

Palateless complete overdenture construction

For each participant, a close fit acrylic resin (Acrostone, England) custom tray with four openings opposite to implant balls was constructed. Mucosa was recorded in a functional state using zinc oxide impression material (Cavex Holland BV, Netherlands) under firm finger pressure, excess at tray holes was trimmed, socket spacers (Dentium Co., Ltd., Korea) were fitted over implant balls, and the tray was reseated intra-orally. Low viscosity polysiloxane impression material (Hydro, DETAX, Ettlingen, Germany) was injected through tray holes over socket spacers to record implants passively.

Construction of palateless denture was done according to principles applied by Farmer and Connelly. [18] Female housings (Slim One Body Ball Socket with O-ring [BPF3], Dentium, Korea) were assembled over ball heads after applying circular pieces of rubber dam to prevent escape of pickup material to ball undercuts. Complete freeing around female housings in denture's intaglio surface was already created by the socket spacers. Vents were drilled into denture's palatal flange to release excess pickup material. Direct intraoral pick up was done while the participant was biting in centric occlusion. After complete setting of cold cure acrylic resin, excess resin flashes in denture's intaglio surface as well as excess resin released from palatal vents were removed [Figure 3].
Figure 3: Intaglio surface of palateless overdentures with O-rings attached. (a) G1. (b) G2

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Evaluation of prosthesis retention

Retention measurements were made 1-day after attachment pickup procedure. Four U-shaped wire loops (Ø 0.9 mm) with retentive tags were attached via cold cure acrylic resin to denture's polished surface, palatal to canines and second molars in agreement with Rutkunas et al.[19] who considered canines and second molars as reliable points for measuring denture retention. U-shaped loops on both sides of the denture were connected with soft wires (Remanium, Ø 0.5 mm, DENTAURUM, Germany) as follows:

Centrally looped anterior wire to measure anterior retention, centrally looped posterior wire to measure posterior retention, centrally looped lateral wires to measure lateral retention on both sides, and two diagonal wires meet in a crossing point to measure central retention [Figure 4]. Retention was estimated by a digital force gauge (Mecmesin, USA) used to record maximum dislodging forces [Figure 5].
Figure 4: (a) Anterior and posterior centrally looped wires. (b) Centrally looped lateral wires. (c) Two diagonal wires meet in a crossing point

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Figure 5: Compact digital forcemeter

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Lower dentures of participants were duplicated in transparent heat cured acrylic resin (Acrostone, England) to verify intimate contact between denture's intaglio surface and the underlying bearing mucosa during retention measurements. A solid rod with a movable pulley was attached to the mandibular transparent teeth using cold cure acrylic resin. The pulley was centered beneath the loop to be tested while patient's mouth was half opened so that maxillary occlusal plane was 45° to the floor. One end of a thread was tied to the tested loop, then it was passed through the external grooved surface of the pulley, and the other end was tied to the hook of the forcemeter. The thread was pulled by the forcemeter in a direction away from the patient to apply vertical dislodging forces against the upper denture. The rod was attached distal to mandibular second molars while measuring posterior retention, to occlusal surface of mandibular first molars while measuring central and lateral retentions, and distal to mandibular canines while measuring anterior retention [Figure 6].
Figure 6: While measuring posterior retention

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Digital forcemeter was prepared before each measurement so that the unit of measurement was gram. Five measurements with 3 min intervals for recovery were performed for each site (anterior, posterior, lateral and central). Maximum dislodging force was recorded, and then the average of the five readings was calculated.

Statistical analysis

Collected data were statistically analyzed using Statistical Package for Social Science (SPSS) (Ver. 17, IBM corporation). Data were expressed as mean ± standard deviation. Comparisons of the two different groups were performed using an independent t-test. Significance was considered when P < 0.05.

   Results Top

Established pilot study has revealed that the clinical mean values of the maxillary inter-canine, canine-second premolar, and canine first molar distances were 32, 14, and 22 mm respectively. Bone quality and quantity allowed placement of 144 implants without bone grafting or sinus lifting. No implant was lost, all cases have succeeded, and all implants lacked mobility along the entire treatment period. All participants demonstrated good oral hygiene and well tissue health around their implants. None of the participants has dropped out, or has missed appointments. All participants expressed verbal satisfaction, more comfort, better mastication, better taste and thermal sensation with the transition from conventional complete denture to palateless over-denture. The primary advantage of this technique is the lower cost when compared to maxillary fixed prosthesis that needs placement of additional implants. In addition, this design has provided satisfactory outcomes regarding retention and stability.

Independent t-test has revealed that the difference in inter-implant distances between G1 and G2 has affected prosthesis retention significantly. [Table 1] shows the mean retention values of G1 versus G2 at different sites (anterior, posterior, lateral and central). Anterior mean retention value was significantly higher in G1 (P = 0.001), while posterior, lateral, and central mean retention values were significantly higher in G2 (P = 0.001).
Table 1: Comparisons for mean retention values of G1 versus G2 measured in grams

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   Discussion Top

Palateless dentures were declared by many investigations to be lighter, more comfortable, provide better stereognosis, tongue recognition, taste and temperature perception, as well as more effective swallowing, phonation, and mastication. [20],[21],[22],[23],[24],[25] Palateless implant overdentures were approached to compensate for limited physical means of retention of palateless dentures caused by lack of maximum palatal coverage. [1],[8],[26],[27] For overdenture design without palatal coverage, a minimum of four implants is a must so stresses over each implant would be clinically acceptable. [4],[5],[6],[7],[8],[26] Since, it is important for patients to perceive their dentures highly retentive, initial retention values of palateless implant overdentures constructed at different inter-implant distances were compared to meet psychodynamic needs of the patients.

The clinical mean value of the maxillary inter-canine distance revealed by the pilot study was 32 mm. That agreed with the results obtained by Dahri et al.[28] who reported a range of 25-32 mm, Craig and Kouble [29] whose resultant range was from 30 to 35 mm, and Khandelwal et al.[30] who claimed a range from 32 to 35 mm. Canine-second premolar and canine-first molar distances have not been investigated before. Their values were revealed by precisely following the measuring regime recommended by Michelinakis et al.[16]

The 100% success rate of all cases may be attributed to proper case selection, sufficient implant number, diameter and length, favorable AP spread of implants so favorable distribution of occlusal loads, and finally proper incorporated surgical and prosthetic procedures including under-sizing of osteotomies, avoiding countersinking to engage crestal cortical bone so better primary stability, and the use of progressive implant loading protocol recommended by many authors. [8],[17]

All participants preferred the decreased palatal coverage as provided them with lighter restorations and more room for their tongues, enabled them to better appreciate texture, taste and temperature of food, in addition to enhanced speech due to the reduced palatal bulk. These findings are the same as Cavallaro and Tarnow [8] and de Albuquerque et al.[31]

This study has revealed that implant location as well as inter-implant distances play a significant role in prosthesis retention, in agreement with several researches. [16],[32],[33] For anterior para-axial rotational retention, G1 showed significantly greater mean value than G2. This may be attributed to implants in G1 were closer to the point of force application than implants in G2. This agrees with Rutkunas et al.[19] who have measured rotational retention of two implant overdentures using different attachments screwed to canine implants with dislodging forces were applied through hooks attached to artificial canines and second molars. For most attachments, anterior retention where dislodging forces were applied in proximity to canine implants was greater than posterior retention where forces were applied away from the installed implants.

For posterior para-axial rotational retention, G2 showed significantly greater retention mean value than that of G1. This may be attributed to many factors: (1) The proximity of posterior implants in G2 to point of force application than in G1, (2) the resultant second class lever where anterior canine implants act as fulcrum (F), second premolar and first molar implants are the resistance (R), and central loop of the posterior wire where dislodging forces were applied is the force (E). Since, the resistance arm of G2 was longer than that of G1, G2 participants have better resisted the posterior dislodging forces.

For lateral para-axial rotational retention, G2 with greater inter-implant distance between anterior and posterior implants has shown significantly higher lateral retention than G1. That means the longer the distance between two O-rings at one side, the greater is the lateral retention on that side, and that agreed with Michelinakis et al. [16] who have revealed that retention of two ball/socket attachments was greater at 29 mm inter-implant distance than at 19 and 23 mm inter-implant distances, and with Tabatabaian et al.[33] who have reported that two ball/socket attachments retaining overdenture showed significantly greater resistance to dislodging forces at 35 mm inter-implant distance than at 15 and 25 mm inter-implant distances.

Theoretically, central axial retention of prosthesis is expected to be the sum of its anterior, posterior, and lateral retentions. Since, G2 has significantly greater posterior and lateral retentions, it is reasonable to have a greater central axial retention as well.

The results of this study may be attributed to the mechanical nature of O-ring attachments, so it is recommended to support this study with other researches using other types of attachments.

   Conclusion Top

For palateless complete implant overdentures retained by four O-ring attachments, favorable AP spread of implants by increasing the inter-implant distance between anterior and posterior implants is recommended to increase prosthesis retention.

Palateless implant overdenture is treatment of choice for patients suffering from the complete palatal coverage of the maxillary dentures.

The high success rate of all cases makes the progressive implant loading protocol more promising and trusted when treating similar cases.

   References Top

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]

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