Table 1 Studies comprising in vitro model experiments

Hegazy [18]

34, 35, 36, 37 and 44, 45, 46, 47

Class 1

Acrylic resin

Silicone impression material

2-mm-thick silicone layer

Group 1: Claspless sub-group A: horizontal bracing arms sub-group B: vertical bracing arms

Group 2: an RPI clasp.

Cobalt–chromium alloy metal frame

Helix ART, Dyna Dental Engineering

Group 1: 34, 44

Group 2: 36, 46

Ball-abutment

Matsudate [17]

45, 46, and 47

Class 2

Epoxy resin model (D50–520; Nissin, Kyoto, Japan)

Approximately 0.5-mm-thick, silicone impression material

Approximately 2-mm-thick silicone impression material

RPI clasp

Lingual plate, double Akers clasp for the left second premolar and first molar

Standard RN

45 or 47

Ball attachment

ELsyad [19]

(Two patterns) 35, 36, and 37 and 45, 46, and 47 or 34, 35, 36, and 37 and 44, 45, 46, and 47

Class 1

Acrylic resin model

Not described

2-mm-thick self-cure silicon layer

No clasps were used (rest only)

Lingual bar

Laboratory implants (TioLogic; Dentaurum, Ispringen, Germany): 3.7 × 13 mm

Group 1: 34 and 44 or 37 and 47

Group 2: 35 and 45 or 37 and 47

Ball-socket attachments

Kihara [20]

45, 46, and 47

Class 2

Acrylic resin model (E50–520, NISSIN, Kyoto, Japan)

1.0-mm-thick polyvinyl siloxane impression material

2-mm-thick polyvinyl siloxane impression material

Akers clasp

Lingual plate, a double Akers clasp for the left second premolar and first molar

Zimmer Biomet Dental, Palm Beach Gardens, FL, USA: 3.75 × 10 mm

46 and 47

A temporary healing abutment with a 4.0 mm height

Rungsiyakull [21]

35, 36, and 37 and 45, 46, and 47

Class 1

Acrylic resin model

Silicone impression material

2-mm-thick silicone layer

Rest-Proximal plate–Akers clasps

Lingual bar

Mini-implants (PW+, Nakhon Pathom, Thailand): 2.75 × 10 mm

35 and 45, or 36 and 46 or, 37 and 47

Equator attachments

Naing [22]

34, 35, 36, 37, and 44, 45, 46, 47

Class 1

Acrylic resin (Nissin E1–550)

Not described

2-mm-thick silicone layer (Exahiflex; GC)

Rest-proximal plate–Akers clasps

A lingual bar and a free-end saddles

BL tapered SLA, Straumann (10 × 4.1 mm)

34 and 44, or 37 and 47

Locator attachments and Magnetic attachments

Hegazy [18]

70 N, vertical, four points bilaterally or two points unilaterally (second premolar and first molar)

Eight self-protected linear strain gauges (Tokyo Sokki Kenkyujo) were cemented onto the buccal and lingual surfaces of the abutment teeth and implants

Stress transmitted to the abutment tooth and implant in the distal implant IARPD was significantly smaller than those of mesial implant IARPD

Matsudate [17]

100 N, vertical, one point (right M1 on denture), unilateral

Piezoelectric 3D force transducers (Kistler Instruments AG, Winterthur, Switzerland) were used to measure the tooth and implant load

A pressure-sensitive tactile sensor film (I-SCAN; Nitta, Osaka, Japan) was used to measure the pressure on the mucosa

The load on the abutment tooth was larger with distal implant-supported RPD than with CRPD

Distal implant-supported RPD greatly reduced the load beneath the denture base

The lateral component of the load that was exerted on the abutment tooth and the implant was larger with mesial implant-supported RPD than with distal implant-supported RPD

ELsyad [19]

60 N, vertical, one point (right M1 on denture), unilateral

Three linear strain gauges (Kyowa Electronic Instruments Co, Ltd, Tokyo, Japan) were cemented at each implant’s buccal, lingual, and distal surfaces at the loading and non-loading sides

The distal implant position showed significantly higher peri-implant stresses than the mesial implant position

Kihara [20]

100 N, vertical, comparing three points (#45, #46 and #47), unilateral

Four strain gauges (KYOWA electric-corporation, Tokyo, Japan) were attached to the implant and tooth root surface

Bending moments of the abutment tooth and implant were significantly higher in mesial implant than in distal implant-supported PRD

The largest mesio-distal displacement of the abutment tooth was observed in mesial implant-supported RPD under #47 loading. In mesial implant-supported RPD, a higher bending moment of the abutment tooth under #45 and #47 loading was detected, although the bending moment in distal implant-supported RPD was almost zero

Bending moments in the implant in mesial implant-supported RPD were statistically larger than distal implant-supported RPD under all loading conditions

Rungsiyakull [21]

150 or 200 N, vertical, four points bilaterally or two points unilaterally (second premolar and first molar)

Twelve strain gauges (Kyowa Electronic Instruments Co, Ltd, Tokyo, Japan) were bonded on the mesial and distal surfaces of the model adjacent to the first thread region of each dental mini-implant, 1 mm away from the implant body and perpendicular to the occlusal plane

Two strain gauges were bonded on the buccal surface and parallel to the long axis of the primary abutment tooth

A mesially placed implant decreased microstrains around abutment teeth compared to a distally placed dental mini-implant

A distally placed implant decreased microstrains around the dental mini-implant itself

Naing [22]

120 N, vertical, one point (right first molar on denture), unilateral

The fine lead wires of the strain gauges (Kyowa Electronic Instruments, Tokyo, Japan) were attached to the flattened and smoothed surface of the experimental model at the mesial, distal, buccal, and lingual sides of each implant

On the loading sides, a larger strain around the implant was observed in the implant at the molar area than in the premolar area

The maximum principal strain (MPS) was distolingually distributed on the loading side under all experimental conditions. On the non-loading side, the MPS distribution of the molar IARPD with the locator attachment was in the distolingual direction. In contrast, the MPS distributions of the other experimental conditions were mesiolingually distributed