Combination of straight and tilted implants for supporting screw-retained dental prostheses in atrophic posterior maxillae: A 2-year prospective study

Abstract

Objectives

To evaluate the two-year survival rate (SR) and marginal bone loss (MBL) of fixed dental prostheses (FDPs) supported by straight (S) and tilted (T) implants under the influence of diverse study variables.

Methods

A prospective investigation comprising 21 patients provided with a total of 27 maxillary screw-retained restorations fixed to 70 dental implants was developed. Two groups of implants were considered depending on their inclination with respect to the occlusal plane: Group 1 (S, n = 37): straight/axial implants and Group 2 (T, n = 33): tilted/angled fixations. Each FDP was supported by a combination of S and T implants. SR and MBL were assessed at the time of loading and two years after surgery. Patient-, surgical- and/or rehabilitation-related information was gathered. Data were statistically analysed at the α = 0.05 significance level.

Results

After 24 months, a 100% SR was achieved and the MBL of S and T implants were statistically similar. T implants located in the molar region showed lower MBL than did those replacing premolars ( p = 0.031).

Conclusions

Upright and angled fixations inserted at posterior maxillary areas resulted in comparable survival rates and peri-implant MBL after two years. The marginal bone resorption around tilted implants depended on their location.

Clinical significance

Screw-retained restorations fixed to straight and tilted implants seem to be a safe treatment option in posterior atrophic maxillae.

Introduction

Posterior tooth loss leads to a series of anatomical changes that create a significant obstacle to restoring free-end edentulous spaces of atrophic jaws . As a result, the chewing ability, aesthetics and social relations of these partially edentate patients may be impaired .

According to the classification of Lekholm and Zarb , the bone quality types III and IV are the most common in the posterior maxilla. The functional occlusal forces are much higher in the molar region than in the anterior sectors . Moreover, there is a significant lack of bone availability after tooth loss in this location due to both the pneumatisation of the maxillary sinus and the centripetal and vertical bone resorption process , which results in unfavourable crown–implant ratios in the posterior maxillary zone as the maxilla is less dense than the mandible .

The literature has described numerous techniques attempting to circumvent the anatomical and physiological difficulties caused by tooth loss in the posterior maxilla . Of these methods, the following are worth mentioning: cantilevered implant-supported fixed dental prostheses (FDPs) ; sinus lifting, using either a lateral window or an osteotome procedure with a crestal approach ; bone grafting ; osteodistraction ; short , pterygoid , or zygomatic implants and, finally, the use of tilted implants .

Several authors have suggested the effectiveness of angled fixations (placed distally, either parallel to the anterior wall of the maxillary sinus or mesial to the mental foramen nerve) in avoiding vital structures and obtaining greater anchorage to the cortical bone . The theory behind this philosophy is that a greater anterior–posterior position of the implant distributes the occlusal forces; therefore, the transverse force placed on the tilted implants is not detrimental to them. In the maxilla, the distal implants can also be benefitted from the cortical bone wall of the sinus and the nasal fossa .

However, even though this treatment has been proposed as a valid therapeutic alternative that may supply many surgical and prosthetic advantages , there is still insufficient evidence to support its widespread use for the restoration of posterior edentulous areas of atrophic jaws.

Hence, the aim of this paper is to assess the main clinical outcomes of tilted implants when combined with dental implants inserted axially to the occlusal forces in the partial rehabilitation of resorbed posterior maxillae two years after surgery.

The null hypotheses tested after two years of follow-up were that a) neither the implant survival rate (SR) nor the peri-implant marginal bone loss (MBL) are influenced by the implant inclination with respect to the occlusal plane ( i.e., straight or tilted) and that b) the MBL of tilted implants does not depend on patient-, surgical- and/or rehabilitation-related factors.

Materials and methods

Study protocol

Selection criteria and other related considerations

This two-year longitudinal prospective study was carried out at a private practice centre (Córdoba, Spain) with the collaboration of an university research team, who where experts in Oral Surgery (University of Seville, U.S., Spain) and Buccofacial Prostheses (Complutense University of Madrid, U.C.M., Spain).

The inclusion criteria were: a) partially edentulous patients aged 18 years or older, with at least 23 teeth, having missing teeth in the posterior maxilla, who were candidates for a screw-retained FDP fixed to a combination of straight and tilted implants; b) subjects presenting a level of bone atrophy (residual bone <8 mm) under the maxillary sinus that would require either a bone graft to place straight implants or the insertion of tilted implants; c) patients with no medical contraindications for oral surgical procedures (American Society of Anesthesiologists: ASA Class 1 or 2) a ; d) subjects with full-mouth plaque scores and full-mouth bleeding scores of less than 25% at baseline; e) patients who understood the study and voluntarily signed an informed written consent to participate and f) subjects attending their clinical and radiographic follow-up appointments.

Patients were excluded based on any disease, condition, or medication that might compromise the osseointegration of the implants, such as: a) presence of active infection or swelling at the site of implant placement (in these cases, the infection was controlled prior to the surgery); b) presence of serious illness such as uncontrolled diabetes, autoimmune diseases, or severe blood-clotting problems; c) patients who had undergone radiation therapy in the head or neck in the past 12 months; d) patients to be restored with tilted implants both in the maxilla and the mandible (to avoid misinterpretation of the findings); e) pregnant women; f) inability or unwillingness to maintain a good level of oral hygiene; g) incapability or refusal to return for follow-up visits; h) cognitive impairment and/or h) motility disorders.

Patients meeting the selection criteria were invited to take part in this trial, which was developed between January of 2014 and December of 2016. All placed implants were somewhat angulated to the occlusal plane. However, this investigation took into consideration the definition of ‘angled implant’ proposed by Aparicio et al. : ‘an implant having an inclination greater than 15° in relation to the occlusal plane, whether in a mesio-distal, disto-mesial and/or bucco-palatal direction’ .

Two brands of dental implants were utilised: (a) Biomet 3i (Dental Ibérica, Barcelona, Spain) and (b) Nobel (Nobel Biocare AB, Göteborg, Sweden). Five models of Biomet 3i with slight differences in configuration were used: OSSEOTITE Parallel Walled; Full OSSEOTITE Parallel Walled; NanoTite Parallel Walled; OSSEOTITE Tapered and OSSEOTITE Parallel Walled Certain; while the Nobel implants were all NobelSpeedy Groovy RP. The best indicated implant type (according to their features and the patients’ conditions) were selected in each case after the research team reached a consensus in a planning session.

This study was conducted in full accordance with the Code of Ethics of the World Medical Association (Declaration of Helsinki); b the Spanish Law 14/2007 for Biomedical Research; c and the Uniform Requirements for manuscripts submitted to Biomedical journals. d The approval of the Ethics Committee of the University of Seville (U.S., Spain) was obtained after the ethical board completed an independent review of the research protocol. The study was undertaken with the informed written consent of each participant. The privacy rights of the patients were always observed.

Surgical interventions

After applying local anaesthesia, the surgical area was prepared following the standard protocol for implant placement . Thereafter, a slightly palatal mid-crestal incision was made, extending it into the gingival sulcus of the adjacent teeth and towards the tuberosity area. A full-thickness mucoperiosteal flap was reflected from the incision. The vestibular bone was exposed at the level of the maxillary sinus wall. Using the information from the radiological study, a lance drill was utilised to reach the maxillary sinus, whose anterior wall was explored with a Naber’s probe. The most distal implant (T) was then inserted, following the anatomy of the aforementioned wall, with an angulation between 20° and 45° in relation to the occlusal plane and the implant platform was placed as distal as possible ( Fig. 1 ). Subsequently, the straight implant (S) was inserted, and both fixations were evaluated for primary stability.

Fig. 1
Tilted implant placed parallel to the anterior maxillary sinus wall.

The surgical procedure was concluded by suturing the flap (Gore-Tex sutures, WL Gore & Associates Inc., Flagstaff, AZ, US). The healing period was monitored to ensure infection-free regeneration and soft tissue primary closure. Patients were prescribed twice-daily rinses with 10 ml of 0.12% chlorhexidine solution for 14 days and were reviewed weekly for a month.

Restorative procedures and second-stage surgery

Ten days after surgery, the sutures were removed and acrylic removable partial dentures (RPDs) with wrought-wire clasps were offered to our patients as temporary restorations. The decision to wear a provisional prosthesis during the osseointegration period (or not) was left in their hands.

The second surgery, performed 3 months later, consisted of reflecting the mucosa to connect the healing abutments. In the case of wearing a provisional RPD, the inner surface of the prosthesis was adapted.

Six months after implant placement, the definitive screw-retained FDPs were fabricated (vacuum-cast Co-Cr frameworks coated with feldspathic ceramic; i.e., Heraenium Co-Cr and Hera Ceram; Heraeus- Kulzer, Wehrheim, Germany) and were fixed to the implants. In both study groups, appropriate transfer copings (depending on the implant brand and platform) were used. A single-phase silicone impression technique with individual trays was selected (Imprint II, 3 M ESPE, Flexitime, Heraeus-Kulzer, Wehrheim, Germany). Non-angulated UCLA abutments were connected to the S osseointegrated fixations; while Multiunit Abutments (MUA) either with 30° or 17° low profile pre-angulations were chosen for the T implants. A torque of 35 N/cm was applied to screw the abutments in all cases.

The final metal-ceramic implant-supported rehabilitations were fixed to their respective abutments tightening the screws to 30 N/cm. Both the static dental relationships (maximum intercuspidation) and the dynamic occlusion (canine and anterior guidance) were checked. Prematurities and interferences introduced by the restoration were eliminated.

Given that the implants were functionally loaded with the definitive prostheses six months after the first-stage surgery, this was considered the baseline point for all measurements.

Implant success criteria

According to the criteria defined by Albrektsson et al. , implant success at two-year follow-up included the presence of implant stability, no radiographic evidence of peri-implant radiolucency, no signs or symptoms of infection (e.g., absence of mucosal suppuration), lack of pain and MBL not exceeding 2 mm.

Follow-up

The restorations were clinically reviewed every three months for two years. Intraoral digital radiographs (Schick CDR, Schick Technologies, Long Island City, NY, US) were obtained immediately after surgery, at the moment of implant loading ( baseline) and 24 months after the fixations were inserted. Periapical radiographs were taken following a long-cone parallel technique with an occlusal template to assess the changes in marginal bone level over time.

In this study the marginal bone height/level was defined as the distance between the lower edge of the implant platform and the most coronal point of contact between the bone and the fixations ( Fig. 2 ) . Measurements of marginal bone height were taken in mm (rounded to the nearest 0.01 mm) at the mesial and distal aspects of each implant and a mean value was calculated for each implant and for each study group at baseline and after two years of healing to the closest half thread using specific software (Schick CDR, Schick Technologies) managed by the same blinded operator. Consequently, the variable ‘marginal bone loss (MBL)’ was defined as the average difference in marginal bone height recorded between the time of implant loading and two years afterwards.

Fig. 2
Reference point (lower border of the smooth implant collar) indicated as a ‘0′ from which the bone level changes (to the marginal bone-to-implant contact depth) were measured.

As explained below, information on possible modulators of MBL was also gathered.

a ) Patient-dependent variables : age, gender, smoking habits (smoker, former smoker, or non-smoker), medical condition (patients on medication or not), bone quality/type according to the Lekholm and Zarb classification , shape of the alveolar ridge according to the classification of Misch and Judy and type of antagonist.

b ) Surgical and/or rehabilitation-dependent variables : implant brand/model (mainly determined by the position of the implant platform), implant length, location (premolar or molar) and wearing or not a provisional prosthesis (acrylic RPD).

Statistical analysis

The data collected were analysed according to well-established statistical methods used in related research . Descriptive statistics (mean and standard deviation: SD) were calculated for all of the study variables . The intra-examiner error was determined by the Kappa test . The normal data distribution was confirmed by the Kolmogorov-Smirnov test and the homogeneity of variances was verified according to the Levene’s test .

Survival rates of S and T implants were compared using the X 2 and the Fisher’s exact tests .

The differences in MBL among S and T implants were evaluated using a two-tailed Student’s t -test with the patient being the statistical unit as the assumption of implant independence within the same patient was inapplicable .

To investigate the statistical significance of possible modulating factors on MBL, the Student’s t -test was utilised for bi-categorical variables and an ANOVA with Bonferroni’s post-hoc test was run to assess the differences in multi-categorical factors .

The statistical analyses were applied according to the requirements for the design of clinical trials in implant dentistry revised at the 8th European Workshop on Periodontology as well as the recommendations of Hannigan and Lynch for oral and dental research . Data were processed using the Statistical Package for the Social Sciences (software v.22) (SPSS/PC+, Inc.; Chicago, IL, USA) taking in advance the cut-off level for statistical significance at α = 0.05 .

Materials and methods

Study protocol

Selection criteria and other related considerations

This two-year longitudinal prospective study was carried out at a private practice centre (Córdoba, Spain) with the collaboration of an university research team, who where experts in Oral Surgery (University of Seville, U.S., Spain) and Buccofacial Prostheses (Complutense University of Madrid, U.C.M., Spain).

The inclusion criteria were: a) partially edentulous patients aged 18 years or older, with at least 23 teeth, having missing teeth in the posterior maxilla, who were candidates for a screw-retained FDP fixed to a combination of straight and tilted implants; b) subjects presenting a level of bone atrophy (residual bone <8 mm) under the maxillary sinus that would require either a bone graft to place straight implants or the insertion of tilted implants; c) patients with no medical contraindications for oral surgical procedures (American Society of Anesthesiologists: ASA Class 1 or 2) a ; d) subjects with full-mouth plaque scores and full-mouth bleeding scores of less than 25% at baseline; e) patients who understood the study and voluntarily signed an informed written consent to participate and f) subjects attending their clinical and radiographic follow-up appointments.

Patients were excluded based on any disease, condition, or medication that might compromise the osseointegration of the implants, such as: a) presence of active infection or swelling at the site of implant placement (in these cases, the infection was controlled prior to the surgery); b) presence of serious illness such as uncontrolled diabetes, autoimmune diseases, or severe blood-clotting problems; c) patients who had undergone radiation therapy in the head or neck in the past 12 months; d) patients to be restored with tilted implants both in the maxilla and the mandible (to avoid misinterpretation of the findings); e) pregnant women; f) inability or unwillingness to maintain a good level of oral hygiene; g) incapability or refusal to return for follow-up visits; h) cognitive impairment and/or h) motility disorders.

Patients meeting the selection criteria were invited to take part in this trial, which was developed between January of 2014 and December of 2016. All placed implants were somewhat angulated to the occlusal plane. However, this investigation took into consideration the definition of ‘angled implant’ proposed by Aparicio et al. : ‘an implant having an inclination greater than 15° in relation to the occlusal plane, whether in a mesio-distal, disto-mesial and/or bucco-palatal direction’ .

Two brands of dental implants were utilised: (a) Biomet 3i (Dental Ibérica, Barcelona, Spain) and (b) Nobel (Nobel Biocare AB, Göteborg, Sweden). Five models of Biomet 3i with slight differences in configuration were used: OSSEOTITE Parallel Walled; Full OSSEOTITE Parallel Walled; NanoTite Parallel Walled; OSSEOTITE Tapered and OSSEOTITE Parallel Walled Certain; while the Nobel implants were all NobelSpeedy Groovy RP. The best indicated implant type (according to their features and the patients’ conditions) were selected in each case after the research team reached a consensus in a planning session.

This study was conducted in full accordance with the Code of Ethics of the World Medical Association (Declaration of Helsinki); b the Spanish Law 14/2007 for Biomedical Research; c and the Uniform Requirements for manuscripts submitted to Biomedical journals. d The approval of the Ethics Committee of the University of Seville (U.S., Spain) was obtained after the ethical board completed an independent review of the research protocol. The study was undertaken with the informed written consent of each participant. The privacy rights of the patients were always observed.

Surgical interventions

After applying local anaesthesia, the surgical area was prepared following the standard protocol for implant placement . Thereafter, a slightly palatal mid-crestal incision was made, extending it into the gingival sulcus of the adjacent teeth and towards the tuberosity area. A full-thickness mucoperiosteal flap was reflected from the incision. The vestibular bone was exposed at the level of the maxillary sinus wall. Using the information from the radiological study, a lance drill was utilised to reach the maxillary sinus, whose anterior wall was explored with a Naber’s probe. The most distal implant (T) was then inserted, following the anatomy of the aforementioned wall, with an angulation between 20° and 45° in relation to the occlusal plane and the implant platform was placed as distal as possible ( Fig. 1 ). Subsequently, the straight implant (S) was inserted, and both fixations were evaluated for primary stability.

Fig. 1
Tilted implant placed parallel to the anterior maxillary sinus wall.

The surgical procedure was concluded by suturing the flap (Gore-Tex sutures, WL Gore & Associates Inc., Flagstaff, AZ, US). The healing period was monitored to ensure infection-free regeneration and soft tissue primary closure. Patients were prescribed twice-daily rinses with 10 ml of 0.12% chlorhexidine solution for 14 days and were reviewed weekly for a month.

Restorative procedures and second-stage surgery

Ten days after surgery, the sutures were removed and acrylic removable partial dentures (RPDs) with wrought-wire clasps were offered to our patients as temporary restorations. The decision to wear a provisional prosthesis during the osseointegration period (or not) was left in their hands.

The second surgery, performed 3 months later, consisted of reflecting the mucosa to connect the healing abutments. In the case of wearing a provisional RPD, the inner surface of the prosthesis was adapted.

Six months after implant placement, the definitive screw-retained FDPs were fabricated (vacuum-cast Co-Cr frameworks coated with feldspathic ceramic; i.e., Heraenium Co-Cr and Hera Ceram; Heraeus- Kulzer, Wehrheim, Germany) and were fixed to the implants. In both study groups, appropriate transfer copings (depending on the implant brand and platform) were used. A single-phase silicone impression technique with individual trays was selected (Imprint II, 3 M ESPE, Flexitime, Heraeus-Kulzer, Wehrheim, Germany). Non-angulated UCLA abutments were connected to the S osseointegrated fixations; while Multiunit Abutments (MUA) either with 30° or 17° low profile pre-angulations were chosen for the T implants. A torque of 35 N/cm was applied to screw the abutments in all cases.

The final metal-ceramic implant-supported rehabilitations were fixed to their respective abutments tightening the screws to 30 N/cm. Both the static dental relationships (maximum intercuspidation) and the dynamic occlusion (canine and anterior guidance) were checked. Prematurities and interferences introduced by the restoration were eliminated.

Given that the implants were functionally loaded with the definitive prostheses six months after the first-stage surgery, this was considered the baseline point for all measurements.

Implant success criteria

According to the criteria defined by Albrektsson et al. , implant success at two-year follow-up included the presence of implant stability, no radiographic evidence of peri-implant radiolucency, no signs or symptoms of infection (e.g., absence of mucosal suppuration), lack of pain and MBL not exceeding 2 mm.

Follow-up

The restorations were clinically reviewed every three months for two years. Intraoral digital radiographs (Schick CDR, Schick Technologies, Long Island City, NY, US) were obtained immediately after surgery, at the moment of implant loading ( baseline) and 24 months after the fixations were inserted. Periapical radiographs were taken following a long-cone parallel technique with an occlusal template to assess the changes in marginal bone level over time.

In this study the marginal bone height/level was defined as the distance between the lower edge of the implant platform and the most coronal point of contact between the bone and the fixations ( Fig. 2 ) . Measurements of marginal bone height were taken in mm (rounded to the nearest 0.01 mm) at the mesial and distal aspects of each implant and a mean value was calculated for each implant and for each study group at baseline and after two years of healing to the closest half thread using specific software (Schick CDR, Schick Technologies) managed by the same blinded operator. Consequently, the variable ‘marginal bone loss (MBL)’ was defined as the average difference in marginal bone height recorded between the time of implant loading and two years afterwards.

Fig. 2
Reference point (lower border of the smooth implant collar) indicated as a ‘0′ from which the bone level changes (to the marginal bone-to-implant contact depth) were measured.

As explained below, information on possible modulators of MBL was also gathered.

a ) Patient-dependent variables : age, gender, smoking habits (smoker, former smoker, or non-smoker), medical condition (patients on medication or not), bone quality/type according to the Lekholm and Zarb classification , shape of the alveolar ridge according to the classification of Misch and Judy and type of antagonist.

b ) Surgical and/or rehabilitation-dependent variables : implant brand/model (mainly determined by the position of the implant platform), implant length, location (premolar or molar) and wearing or not a provisional prosthesis (acrylic RPD).

Statistical analysis

The data collected were analysed according to well-established statistical methods used in related research . Descriptive statistics (mean and standard deviation: SD) were calculated for all of the study variables . The intra-examiner error was determined by the Kappa test . The normal data distribution was confirmed by the Kolmogorov-Smirnov test and the homogeneity of variances was verified according to the Levene’s test .

Survival rates of S and T implants were compared using the X 2 and the Fisher’s exact tests .

The differences in MBL among S and T implants were evaluated using a two-tailed Student’s t -test with the patient being the statistical unit as the assumption of implant independence within the same patient was inapplicable .

To investigate the statistical significance of possible modulating factors on MBL, the Student’s t -test was utilised for bi-categorical variables and an ANOVA with Bonferroni’s post-hoc test was run to assess the differences in multi-categorical factors .

The statistical analyses were applied according to the requirements for the design of clinical trials in implant dentistry revised at the 8th European Workshop on Periodontology as well as the recommendations of Hannigan and Lynch for oral and dental research . Data were processed using the Statistical Package for the Social Sciences (software v.22) (SPSS/PC+, Inc.; Chicago, IL, USA) taking in advance the cut-off level for statistical significance at α = 0.05 .

Results

Description of the whole sample

Two subjects (9%) were excluded from the original reference population ( n = 23) because they were typified as ASA Class 3. The final study sample was composed of 21 patients who had been provided with a total of 27 metal-ceramic screw-retained FDPs fixed to 70 dental implants. None of them were lost during the study. The mean follow-up period was 24.1 ± 1.71 months.

All of the participants were treated with one maxillary posterior FDP supported by a combination of S and T implants. The mean age of the volunteers was 60.7 ± 7.2 years (from 43 to 76 years). Pooling together all of the rehabilitations, two groups of implants were established depending on their inclination with respect to the occlusal plane: Group 1 (S, n = 37): straight/axial implants (53% of the study sample) and Group 2 (T, n = 33): tilted/angled implants (47%; with an average angulation of 32.8° ± 8.4°).

The Kappa statistics showed a perfect intra-assessment coefficient of reliability ( k = 1).

The distribution of patients with reference to the patient-dependent variables and the surgical- and/or rehabilitation-dependent variables is detailed in Table 1 .

Table 1
Influence of the study variables on the marginal bone loss (MBL; mm) of the tested groups ( N = 70).
Study variables (%, n ; total sample) Statistical significance of MBL (mm)
Straight (S) implants (controls) (52.9%, n = 37) Tilted (T) implants (47.1%, n = 33) Total sample (S + T) implants (100%, n = 70)
Mean (SD) p- values Mean (SD) p- values Mean (SD) p- values
Group 1: Patient-dependent variables
Age
≤60 years (51%, n = 36) −0.83 (0.96) 0.440 NS (a) −0.65 (1.04) 0.066 NS (a) −0.74 (0.99) 0.062 NS (a)
>60 years (49%, n = 34) −0.60 (0.80) +0.01 (0.98) −0.31 (0.93)
Gender
Female (53%, n = 37) −0.69 (0.60) 0.871 NS (a) −0.32 ± 1.19 0.943 NS (a) −0.51 (0.94) 0.831 NS (a)
Male (47%, n = 33) −0.74 (1.12) −0.34 ± 0.91 −0.56 (1.03)
Smoking habits
Non-smokers (40%, n = 28) −0.57 (0.59) 0.331 NS (b) −0.23 ± 0.82 0.857 NS (b) −0.40 (0.72) 0.570 NS (b)
Former smokers (24%, n = 17) −0.53 (0.59) −0.51 ± 1.06 −0.52 (0.79)
Smokers (36%, n = 25) −1.01 (1.24) −0.34 ± 1.34 −0.69 (1.31)
Being medicated or not
Yes (69%, n = 48) −0.60 (0.65) 0.244 NS (a) −0.28 ± 1.09 0.683 NS (a) −0.44 (0.89) 0.265 NS (a)
No (31%, n = 22) −0.96 (1.24) −0.44 ± 0.99 −0.73 (1.14)
Bone quality type (Lekholm & Zarb classification)
Type I density (0%, n = 0) 0.040 * (b)
II <III *
0.565 NS (b) 0.167 NS (b)
Type II density (78%, n = 54) −0.57 (0.82) −0.22 ± 1.14 −0.41 (0.98)
Type III density (11%, n = 8) −1.86 (1.04) −0.46 ± 0.40 −0.98 (0.96)
Type IV density (11%, n = 8) −0.97 (0.73) −0.82 ± 1.12 −0.89 (0.88)
Shape of the alveolar ridge (Misch & Judy classification)
Type A (9%, n = 6) −1.06 (1.29) 0.214 NS (b) −0.51 ± 0.33 0.160 NS (b) −0.87 (1.05) 0.025 * (b)
B < D *
Type B (66%, n = 46) −0.50 (0.59) −0.12 ± 1.03 −0.32 (0.84)
Type C (21%, n = 15) −1.01 (1.37) −0.58 ± 1.03 −0.78 (1.18)
Type D (4%, n = 3) −1.55 (0.38) −2.39 ± 0.00 −1.83 (0.55)
Type of antagonist
FDP supported by S implants (57%, n = 40) −0.74 (0.73) 0.445 NS (b) −0.31 ± 0.86 0.113 NS (b) −0.54 (0.80) 0.001** (b)
Hybrid implant > the other groups*
Hybrid implant prosthesis (3%, n = 2) −4.04 (0.00) −2.94 ± 0.00 −3.49 (0.77)
Implant-retained overdentures (7%, n = 5) −0.02 (0.01) −0.24 ± 0.37 −0.13 (0.30)
Natural dentition (27%, n = 19) −0.56 (0.68) −0.01 ± 1.34 −0.30 (1.05)
Acrylic RPD (6%, n = 4) −0.34 (0.41) −0.74 ± 0.64 −0.54 (0.49)
Group 2: Surgical and/or rehabilitation-dependent variables
Implant brand/model
Biomet 3i-OSSEOTITE PW (56%, n = 39) −0.49 (0.56) −0.24 ± 0.95 −0.39 (0.74) 0.001 ** (b)
NobelSpeedy Groovy RP ≥ OSSEOTITE PW*, Full OSSEOTITE PW*, NanoTite PW*, OSSEOTITE Tapered*
Biomet 3i-Full OSSEOTITE PW (17%, n = 12) −0.82 (0.80) −0.04 ± 1.20 −0.24 (1.13)
Biomet 3i-NanoTite PW (14%, n = 10) −0.79 (1.06) −0.33 ± 0.62 −0.69 (0.90)
Biomet 3i-OSSEOTITE Tapered (6%, n = 4) −0.60 (0.18) −0.40 ± 0.18 −0.50 (0.19)
Biomet 3i-OSSEOTITE PW Certain (4%, n = 3) −1.82 (0.00) −1.12 ± 1.17 −1.35 (0.92)
Nobel Biocare-Speedy Groovy RP (3%, n = 2) −4.04 (0.00) −2.94 ± 0.00 −3.49 (0.77)
Implant length
8.5 mm (10%, n = 7) −0.55 (0.45) 0.613 NS (b) −0.03 ± 0.00 0.224 NS (b) −0.66 (0.66) 0.208 NS (b)
10 mm (7%, n = 5) −1.08 (0.00) −1.21 ± 0.90 −1.18 (0.78)
11.5 mm (16%, n = 11) −0.03 (0.76) −0.31 ± 0.87 −0.23 (0.74)
13 mm (48%, n = 34) −0.65 (0.53) −0.12 ± 1.08 −0.37 (0.95)
15 mm (19%, n = 13) −0.62 (0.67) −0.62 ± 1.10 −0.88 (1.29)
Location
Premolar (53%, n = 37) −0.48 (0.55) 0.09 NS (a) −1.57 ± 1.21 0.031 * (a)
Premolar > Molar
−0.58 (0.69) 0.303 NS (a)
Molar (47%, n = 33) −1.78 (1.60) −0.20 ± 0.97 −0.34 (1.07)
Wearing an acrylic provisional RPD during the osseointegration period
Yes (69%, n = 48) −0.73 (0.72) 0.410 NS (a) −0.29 ± 1.14 0.734 NS (a) −0.90 (0.96) 0.038 * (a)
Yes > No
No (31%, n = 22) −0.22 (0.30) −0.17 ± 0.60 −0.22 (0.30)
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Jun 17, 2018 | Posted by in General Dentistry | Comments Off on Combination of straight and tilted implants for supporting screw-retained dental prostheses in atrophic posterior maxillae: A 2-year prospective study
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