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REVIEW
Year : 2021 | Volume
: 21
| Issue : 1 | Page : 28-44
The rehabilitation of posterior atrophic maxilla by using the graftless option of short implant versus conventional long implant with sinus graft: A systematic review and meta-analysis of randomized controlled clinical trial
Sachin Haribhau Chaware1, Vrushali Thakare2, Ritu Chaudhary3, Ajit Jankar4, Smruti Thakkar1, Sidesh Borse1
1 Department of Prosthodontics, MGVs KBH Dental College and Hospital, Nashik, Maharashtra, India
2 Department of Public Health Dentistry, MGVs KBH Dental College and Hospital, Nashik, Maharashtra, India
3 Department of Prosthodontics, Royal College of Surgeons England, Britannia Dental Surgery, Newport, UK
4 Department of Prosthodontics, MIDSR Dental College, Latur, Maharashtra, India
Correspondence Address:
Prof. Sachin Haribhau Chaware
Department of Prosthodontics, MGVs KBH Dental College and Hospital, Nashik - 422 001, Maharashtra
India
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/jips.jips_400_20
Aim: The purpose of systematic review and meta-analysis was to compare the efficacy of short implant versus conventional long implant with sinus graft in patients rehabilitated for posterior atrophic maxilla.
Setting and Design: Systematic review and meta analysis.
Materials and Methods: Electronic searches were conducted in Pub Med, Embase, and Medline with supplemented by manual search up to December 2019. The randomized controlled trial (RCTs) comparing short implant (<8.5 mm) and long implant (>8.5 mm) with sinus graft were included. (Prospero CRD42020186972).
Statistical Analysis Used: Random-effect model, fixed-effect model, A funnel plot and the Egger's test.
Results: Twenty-two Randomized controlled trials (RCTs) were assessed with 667 patients and 1595 implants (short implant:767, Long implant:835). No significant difference of implant survival rate was recorded for short and long implant (at patient level: RR: 1.01, 95% CI = 0.52-2.0, P = 0.87, I2 = 0%, at implant level RR = 1.09, 95% CI = 0.6-2.0, P = 0.7, I2 = 0%). Similarly marginal bone resorption was reported no difference for short and long implant (MD = 0.16. 95% CI: -0.23 = -0.08, P = 0.00, I2 = 74.83%). Biological complications were marginally higher for long implant (RR = 0.48, 95% CI = 0.23-0.8, P = 0.13, I2 = 29.11%). and prosthetic complications were marginally higher for short implants (RR=1.56, 95% CI=0.85-3.15, P = 0.43, I2 = 0%).
Conclusion: There was no significance difference in implant survival rate and marginal bone resorption recorded for both the short implant and long implant with sinus graft, in the patients rehabilitated with posterior atrophic maxilla. Hence, short implant is a suitable alternative to long implant with sinus graft, for the rehabilitation posterior atrophic maxilla.
Keywords: Bone augmentation, pours bone, short implant, sinus graft, textured implant
Maxillary sinus grafting either by lateral approach or crestal approach is the routine procedure for implant rehabilitation at posterior atrophic maxilla.[1],[2],[3],[4],[5] The sinus grafting accommodates the length of the conventional long implant and increases bone-implant surface contact.[6],[7],[8] The successful healing of the sinus-graft with a minimum reduction of the graft height is the principal determinant of a long-term stability of the sinus-graft implant.[9] The gold standard of sinus graft is the autograft, due its inherent osteogenic potential[10],[11] The implant osseointegrated with sinus autograft have shown the success rate of 82%–96% with mild to moderate reduction of graft height.[12],[13],[14] The major drawback of sinus autograft is high morbidity at the donor site, due to requirement of the additional surgery which leads to subsequent postoperative pain, tissue scaring, patient discomfort and secondary infection[9],[10],[15] Hence, many clinicians preferred to use of an autograft in combination with other bone substitute.[16] The bony substitutes for instance allograft,[16] xenograft,[17],[18] bovine graft materials,[19] platelet-rich fibrin (PRF),[20] and alloplastic materials as synthetic calcium phosphate (β-tricalcium phosphate),[16] hydroxyapatite, biphasic calcium phosphate[16],[18] and Bio-glass[16],[18] have shown higher success rate, either used exclusively or as a mixture with autograft than the 100% autogenous bone.[21]
The most common postgraft complications are sinus membrane perforation, followed by graft infection and inadequate primary stability.[22],[23],[24],[25] However, the Sinus-graft healing period and delayed placement of the implant is the crucial factor, as there is need for the stabilization of the graft for first 6–12-month period because the maximum reduction of the graft height occurs in the first 12 months.[15],[17] Due to prolonged healing period with no contact of prosthesis, perhaps create the problem of mastication and esthetic for the patient rehabilitated with the atrophic maxilla.[15],[16] Similarly, the retrospective analysis (5 years) reported that the higher implant survival rate (ISR) and lower bone resorption for the implant placed in a native bone than the implant placed with sinus graft. Hence many clinicians preferred to select graftless options of implant placement.[15],[25],[26],[27] The graftless options of implant placement are zygomatic or pterygoid bone implant placement and short implant. The zygomatic implant has a success rate of 90%–100%.[15],[29] However, the zygomatic bone implant placement is more invasive procedure hence it needs greater clinical skill.[15],[28] The possible complication associated with the zygomatic implant placement is an extra bulk at the palatal area (palatal emergence profile), which creates discomfort to the patient and difficulty in maintaining the oral hygiene.[29],[30]
Recently, the selection and placement of short implant have gained widespread popularity due to its inherent benefit. Any implant with total length is 8 mm or less, completely submerged in bone is considered as a short implant and implant length <6 mm was referred to as an ultra-short implant.[31] In contrast, few researchers suggested that implant length of 10 mm is consider as a standard length for predictable success and implant below 10 mm considered to be a short implant.[32],[33] The main clinical advantage of short implant that it is noninvasive surgical procedure with no additional grafting procedure required; therefore, it completely eliminates donor site morbidity.[33] Other clinical advantages are it reduces the surgical time,[33],[34] decreases the time-span of implant placement, no damage to adjacent tooth,[35] correct positioning of the implant, fewer postinsertion complications and economical.[36],[37] However, the survival of short implant will be questionable when the factors like crown-implant ratio (C/I), initial implant stability particularly type 4 bone, prosthetic complications, reentry to submerged healing implant at the second stage, and distribution of axial or nonaxial stress particularly in steep compensative curve taken into the consideration.[36],[37] The previous systematic review.[36],[37] Has covered less number of studies and selected patient as a statistical unit, that creates the problem for recording the ISR as the multiple failures in single patient-reported as one failure. The objective of the present systematic review[38],[39] is to evaluate the effectiveness and predictability of short implant versus conventional long implant with sinus graft for the patient rehabilitated with posterior atrophic maxilla by taking patient and implant as the statistical unit.
Materials and MethodsThis systematic review was designed according to the guidelines of the preferred reporting item for systematic review (PRISMA) and meta-analysis guidelines.[40],[41] The systematic review was developed and registered (Prospero Registration number database: CRD42020186972).
A systematic search was conducted to retrieve eligible randomized controlled trial (RCT) up to December 2019 of short implant and conventional long implant with sinus graft. The electronic search was conducted in Medline (PubMed), Cochrane Library (The Cochrane Central Register of Controlled Trials), SCOPUS, Embase, CINHAL, web of science, and Google scholar.
The PICOS protocol for the search engine are as: Population (P): Partially edentulous patients reported for the rehabilitation of posterior maxillary ridge (molar and premolar region) with reduced bone height (RBH). Intervention (I): Simultaneous placement of short implant (<8.5 mm) and conventional long implant (≥8.5 mm) with sinus graft. Comparison (C): Short implant versus conventional long implant with sinus graft at posterior atrophic maxilla. Outcome (O): ISR, Marginal bone resorption (MBR), Biological complication, and Prosthetic complication between short and long implant.
To electronic search was supplemented by manual search of journal-specific area: The manual search list of the collected journal is as follows.
European journal of oral implantology, Journal clinical Periodontology, European Journal of Oral science, Clinical oral Implant research, Med Oral Patol Oral Cir Bucal, Journal Korean association of oral maxillofacial surgery, The Journal of Craniofacial surgery, International Journal of oral and maxillofacial implant, Stomatologija, Baltic Dental and Maxillofacial Journal, Clinical Implant Dental Related Research, Journal of Dental 1reearch, Journal of Dentistry, The open dentistry journal, Oral and Maxillofacial Surgery, and Quintessence International.
The two investigators were searched the articles by screening the title and abstract. The searched analysis based on the following inclusion criteria: the studies included only RCT with no follow-up restrictions. Studies with clear survival rate, failure rate, MBR, and complication associated with implant data. The studies with the comparison of short implant and conventional long implant with graft in a same analysis. The studies with minimum 10 participants in the test and control groups for parallel and split mouth RCT was included in the search. The studies associated with the zygomatic implant, in vitro study, case report, animal study was not included. Similarly, the studies of the short implants without comparison, length of the implant was more than 8.5 mm still it was in the list of short implant, and short implant with sinus elevation or grafting procedure was excluded from the search.
The full-text length of the articles of the selected search was evaluated by three investigators (reproducibility 0.87, Cohen's kappa). The data retrieved from each of the selected study assigned to the comparison of short implant and conventional long implant, length and diameter of the short and long implant, and type of sinus graft/sinus surgery. Patient data such as mean age, male/female ratio, and smoking habits. Publication year, and author. Outcome variable such as follow-up period, loading protocol, survival rate, biological complications, MBR and prosthetic complications.
All three investigators discussed all the variant views of the selected search and any disagreement or variant opinion between three investigators was further resolved by addition of the fourth investigator. Any missing data, author of the study were contacted via E-mail to provide further detail.
Risk of bias was assigned as per the Cochrane collaboration tools[42] (random sequence generation [selection bias], allocation concealment [selection bias], blinding of participants and personnel [performance bias], blinding of outcome assessment [detection bias], incomplete outcome data [attrition bias], selective reporting [reporting bias], and other bias). The investigators were recorded the risk of bias of each individual study and then across the study. If the study fulfils all seven criteria, then it was notifying as a low risk, sequentially, if the study missed one criteria or unclear, then that study was notifying as a moderate risk, and if the study missed two or more criteria, then it was considered as high risk [Table 1] and [Table 2].
The meta-analysis from the Data search was conducted by using software NCSS LIC (NCSS statistical software 2019, v19.0.2, version, www.ncss.com). The outcome variables included ISR, biological complication and prosthetic complications evaluated by risk ratio (RRs). The ISR (implant failure) is a dichotomous variable of each implant group; hence, it is pooled and analyzed by RRs and 95% confidence interval (95% CIs). The value of marginal bone loss as a continuous variable recorded as “standardized mean difference” (SMD) with 95% CI were used. The RRs and SMD values were considered significant when P < 0.05. To find out the heterogeneity among the studies, Cochrane Q test was performed (P < 0.001/CI 95%). The presence of heterogeneity was assessed by using inconsistency test I2 (high heterogeneity: I2 > 75%; low heterogeneity: I2 < 25%). The random-effect model was used when meta-analysis recorded high heterogeneity (P < 0.10).[43] However, fixed-effect model was adopted, when heterogeneity was not statistically significant. A funnel plot and the Egger's test[44] were used to assess the presence of the publication bias.
ResultsThe search process reviewed 68 full-text articles by first and second authors, after the evaluation of the title and abstract (kappa 0.87). The twenty-two articles were evaluated, as per the agreement of the four authors (agreement = 86.6) and proposed inclusion criteria of the review [Figure 1]. The twenty-eight studies were excluded, the reason specified with [Figure 1]. The twenty-two studies.[45],[46],[47],[48],[49],[50],[51],[52],[53],[54],[55],[56],[57],[58],[59],[60],[61],[62],[63],[64],[65],[66] were further divided as per their follow-up period after the prosthetic component loading. The two studies.[45],[46] were reported a 5-year follow-up period, seven studies.[47],[48],[49],[50],[51],[52],[53] were reported a follow-up period of 3 years, eight studies.[54],[55],[56],[57],[58],[59],[60],[61] were reported 1-year follow-up, and five studies were reported.[62],[63],[64],[65],[66] Less than 1-year follow-up. Out of 22 trials, five trials were split-mouth design and 18 trials were parallel design with two groups except one article was having three groups. The pooled analysis geometry reported 704 (short implant group: 419, long implant group: 390) patients, out of 37 patients were dropped during follow-up visit due to various reason. The sample group of Thoma et al.[45] trial was evaluated sequentially after 1 year by Schincaglia et al. (2015)[61] and 3 years by Pohl et al.,[53] hence to eliminate the repetition sample size, the review has selected the sample size of a 5-year evaluation done by Thoma et al.[45] The review eventually assessed the 667 patients for outcome variables. The review analyzed 1595 (short implant: 767, long implant: 835) implants of the clinical trial. The highest follow-up period was 60 months and the lowest follow-up period was 4 months. The length of the short implant ranged from 4 to 8.5 and whereas the conventional long implant ranged from 10 mm to 15 mm. The diameter of both groups ranged from 3.7 mm to 7 mm. [Table 3] describes the methodological aspect of the implant design and the sinus graft and [Table 4] discussed the outcome variables of the comparative studies. The studies were used the commercially available standardized implant system by the various manufacturer and in the sinus graft group, the trial were used xenograft except one study used the autogenous bone graft (iliac crest). Three studies.[45],[53],[61] has reported the C/I ratio.
Table 3: Methodological description of the comparative studies of short implants and long implants with sinus graft
Table 4: Outcome variables of comparative studies of short implant and long implant with sinus graftRisk of bias is specified with [Table 1] and [Table 2]. The eleven studies[45],[49],[50],[51],[52],[53],[54],[57],[58],[59],[60] were assigned as a high risk and seven studies[46],[47],[48],[50],[55],[61],[62] were assigned as an unclear risk for detection bias because the investigator who has given the responsibility to do clinical and radiographic analysis could be easily identified the augmented site due to different implant length and rest of the seven studies show unclear bias as independent examiner perform the clinical and radiological assessment. Two studies[50],[62] show the unclear selection bias as not clearly mentioned about the random sequence generation. Two studies[50],[62] were reported for allocation concealment bias as the studies did not mention the eligible patient consent, opening of opaque sealed envelope and allocation of the patient to the respective surgeon. One study[46] shows a high risk for attrition bias as 11 patients dropped during follow up period and five studies show unclear bias as dropped of 2–3 patients per study. The reporting bias specifically related to two studies[48],[53] in that one study reported selectively the implant thread geometry[50] and other study explained selectively the significance of platelet rich plasma.[48] Remaining five studies[56],[63],[64],[65],[66] were reported low risk for all bias. Funnel plot shows the symmetrical distribution of the studies, indicating the absence of publication bias [Figure 2],[Figure 3],[Figure 4].
Outcome variables
ISR was calculated as a failure rate of the implant within the specified follow-up period mentioned with the individual study. Two studies[45],[46] with 5 years follow-up period reported 100% survival rate for conventional long implant. In contrast, short implant reported marginally lower ISR for the same group (at patient level: RR = 2.8 95% CI = 0.3–29.78 P = 0.3, I2 = 0%, at implant level: RR = 4.1, 95% CI = 0.4–39.64 P = 0.1, I2 = 0%). Studies[47],[48],[49],[50],[51],[52],[53] with 3 years follow-up period were reported no significant difference between short and long implant (at patient level: RR = 1.3, 95% CI: 0.3–5.6, P = 0.6, I2 = 0%, at implant level: RR = 1.8, 95% CI = 0.5–7.1, P = 0.3, I2 = 0%). Three studies[48],[49],[53] were reported 100% ISR for both short and long implant group. The two studies[51],[52] showed 100% ISR for long implant and one study[50] showed 100% ISR for short implant. The three studies[48],[51],[52] reported marginally lower ISR for short implant except one study showed marginally lower ISR for long implant.[50] Similarly, there is no significant difference between short and long implant for the studies[54],[55],[56],[57],[58],[59],[60],[61] with 1 year follow-up period (at patient level: RR = 0.83, 95% CI = 0.3–1.8 P = 0.6, I2 = 0%, at implant level: RR = 0.8 95% CI = 0.4–1.7 P = 0.6, I2 = 0%). Two studies reported.[58],[60] 100% ISR for both short and long implant, three studies[54],[59],[61] reported marginally lower ISR for long implant, except, one study[56] showed marginally lower ISR for short implant, and one more study[57] however, reported equal survival rate for both short and long implant group. In <1 year, only one study[62] showed 100% ISR for both groups, three studies[64],[65],[66] reported marginally lower ISR for short implant and one study[63] showed lowest survival rate among the all the groups, however ISR was lower for long implant. Eventually, the meta-analysis [Table 5] and [Table 6] reported statistically no significant difference in ISR for both short and conventional long implant with sinus augmentation placed for the rehabilitation of posterior atrophic maxilla (at patient level: RR: 1.01, 95% CI = 0.52–2.0, P = 0.87, I2 = 0%, at implant level RR = 1.09, 95% CI = 0.6–2.0, P = 0.7, I2 = 0%). There is no significant difference in ISR for both short and long implant in relation to small to wider diameter of implant (>5 mm).
Table 5: Forest plot of implant survival rate of short implant and long implant at patient level
Table 6: Forest plot of implant survival rate of short implant versus long implant at implant levelMarginal bone resorption
There are 18 studies[46],[47],[48],[49],[50],[51],[52],[53],[54],[55],[56],[57],[58],[59],[60],[61],[63] included for MBR, as the four studies[62],[64],[65],[66] did not report the MBR due to follow up period was <9 months except one study[63] showed MBR with follow-up period was <6 months. The reported mean difference of MBR for the studies[43],[44],[45],[46] with 5 years follow-up period was higher for long implant (MD: = 3.5, 95% CI: −0.57–0.27, P = 0.1, I2 = 61.53%). The reported mean of MBR for the studies with 5 years follow-up was 0.54 mm and 1.93 mm for short implant and 0.46 mm and 2.28 mm for long implant. The mean difference for 3 years follow up study was reported no significant difference for short implant and long implant (MD = 0.15, 95% CI = −0.24–−0.06, P = 0.00, I2 = 91.30%) The average of the means of MBR for the studies[47],[48],[49],[50],[51],[52],[53] with 3 years follow up is 1.01 mm (range 0.20 mm–1.36 mm) for short implant and long implant 1.08 mm (range 0.27–1.74 mm). Similarly, marginally lower MBR for short implant (MD = 0.16, 95% CI = 0.27–0.05, P = 0.00, I2 = 86.09%) the average of means of the studies[54],[55],[56],[57],[58],[59],[60],[61] with 1 year follow-up is 0.75 mm (range 0.1–1.16) for short implant and long implant 0.94 mm (range 0.1–1.53 mm). There are five studies with follow-up <1 year, but only one study[63] reported the MBR, i.e., 0.48 mm for short implant and 0.50 for long implant, remaining four studies do not report the MBR due to follow-up was <6 months. The combined result of 18 studies [Table 7] reported no significant difference in MBR for both short implant and conventional long implant (MD = 0.16. 95% CI: −0.23–−0.08, P = 0.00, I2 = 74.83%).
Table 7: Forest plot of marginal bone resorption of short implant and long implantBiological complication
Fourteen studies[45],[46],[47],[49],[50],[51],[52],[54],[55],[56],[57],[59],[64],[65],[66] reported the biological complications and among them, seven studies showed biological complications associated only with long implant. Short-term complications are pain, swelling, infection hematoma, and bad taste breath. Long-term complications are bleeding on probing, graft failure, peri-implant mucositis, and implant failure. Nine studies reported the sinus membrane perforation, and two studies reported implant dislodged into the maxillary sinus, four studies show long-term peri-implant mucositis and three studies reported bleeding on probing, pocket depth, and plaque control record. The augmented group with long implant shows more complications than short implant without augmentation [Table 8] (RR = 0.48, 95% CI = 0.23–0.8, P = 0.13, I2 = 29.11%).
Table 8: Forest plot of biological complication of short implant versus long implantProsthetic complications
Nine studies[45],[46],[47],[49],[52],[53],[55],[59],[64] reported the prosthetic complications. The listed prosthetic complications are abutment screw fracture, screw loosening, ceramic veneer fracture, debonding, or de-cementation of crown. Short implant reported higher prosthetic complications than conventional long implant [Table 9], (RR = 1.56, 95%CI = 0.85–3.15, P = 0.43, I2 = 0%).
Table 9: Forest plot of prosthetic complications of short implant versus long implantPatient satisfaction (additional analysis)
There were Nine studies[45],[46],[48],[50],[51],[54],[58],[60],[62] that reported the patient satisfaction, out of that three studies[45],[60],[62] reported the patient satisfaction for both short and long implant and six studies[46],[48],[50],[51],[54],[58] reported satisfaction for short implant. Thoma et al.[45] used patient-reported outcome measures to record patient satisfaction and equal satisfaction for both short and long implant. Felice et al.[46] reported that 15 patients were satisfied for short implant and five patients showed equal satisfaction for both short and long implant. Taschieri et al.,[48] Bechara et al.,[50] and Guljé et al.,[60] performed questionnaire survey and proposed more satisfaction for short implant. Gastaldi et al.[51] used functional and esthetic criteria and reported equal satisfaction for both short and long implant and Zhang et al., evaluated by using postoperative clinical symptoms and reported more satisfaction for short implant.
DiscussionThe present review combined the results of 22 RCTs (maximum follow-up is 60 months and minimum follow-up is 120 days) with 704 participants and 1595 implants and synthesized the information of outcome variables. There was no difference of outcome variables between short and conventional long implants with sinus graft. The synthesized information derived from outcome variables are discussed in the following way.
Implant survival rate
The analysis (patient level and implant level) of ISR reported that out of 22 trial 7 studies showed 100% survival rate. There was 21 (36.52%) short implant and 20 (41.75%) long implant failed to osseointegrate. At the patient level, 15 (27.93%) patients with short implant and 14 (27.85%) patient with long implant showed failure. It is concluded that there is no significant difference of ISR in both short and long implant. The finding of the present review was similar to the previous systematic review.[36],[37] However, the previous review recorded the ISR at the patient level, but the multiple failure of implant in one patient was recorded as a one.[67] Hence, the present review implemented both the methods to calculate ISR.
It is kind to measure the factors that improve the survival rate of short implant. In the past, Misch[68] and Lekholm et al.[69],[70] reported that high failure of short implant <10 mm in posterior maxilla due to the porous bone and greater biting strength. The significant factor noticed by the present review is the surface coating or textured surface of the implant. The surface coating on the implant is vary from the roughened grit-blasted surface.[46] Sandblasted surface (optima),[47],[48] sand-blasted and acid-etched surface, hydroxyapatite coating, calcium incorporated hydroxyapatite coating, nanostructured calcium incorporated titanium surface (Xpeed)[64] sanded with hydroxyapatite particles. Straumann (SLActive).[62] The remarkable feature of rough surface implant that it increases the bone-implant contact and initial stability,[71] thereby, it promotes the osteoconduction,[72] contact osteogensis, and rapid osseo-integration.[73] It offers greater torque resistance.[74] and the stress transformation from implant to bone is influenced by surface roughness.[75] The combination of nanostructured calcium surface and hydroxyapatite surface enhances rapid protein adhesion and subsequent osteoprogenitor cell attachment, proliferation, differentiation, and spreading.[64] The hydrophilic implant (SL active Straumann) increases the bone-implant contact and achieved initial stability during the healing period.[62],[76] Implant hydrophilic surface possess high surface energy that improves bone regeneration and clot stabilization.[62],[76] Bechara et al.[50] proposed in his investigation that implant thread geometry influences the primary stability as it increases the surface area and bone-implant contact. The thread depth distance has a partial impact on the surface area. The sharp – square-shaped thread deigned used in the study offers greater resistance to compressive and minimize share force. Taschieri et al.[48] investigated Platelet-rich fibrin (PRF) as a liquid form applied before the placement of short implant, which was already sandblasted. The author assumed that it increases the biological activity and proliferation and differentiation of osteoproginator cells as well as osteoblast. Bechara et al.[50] reported that both short and long implants achieved acceptable implant stability (>58 IQ). A similar observation was also made by Zhang et al.,[62] in that implant stability was measured 69.76 + 6.24 mean/standard deviation (SD) implant stability quotient (ISQ) for short implant (6 mm), 66.99 + 5.93 mean/SD ISQ for short implant (8 mm) with osteotome sinus floor elevation (OSFE) and 77.72 + 4.95 mean/SD ISQ for long implant (10 mm) with OSFE at initial implant placement. There was no significant difference between short and long implant at initial implant stability. Eventually, the review observed that the reason of the failure of earlier short Brenamark type implant was due to minimally rough surface of pure titanium machined turned implant, that does not produce even and less bone–implant contact and offers less resistance to horizontal forces.[77],[78],[79] The long-term data proposed by Thoma et al. (2018)[45] and Felice P (2019)[46] reported a predictable survival rate of the short implant. The review observation was further supported by a Lee et al.,[80] the author claimed that a sand-blasted, large-grit, acid-etched surface of the implants, submerged subcrestally produces excellent survival rate of 98.3% at posterior maxilla. Similarly, Hagi et al.[81] was also highlighted the implant thread geometry and its significance to the primary stability of the implant. The survival rate reported by Resonance frequency testing does not show a significant difference between short and long implant. Eventually, it has been proved histologically, that bone implant contact was more favourable on the rough surface implant in contrast to the smooth surface implant.[82]
Marginal bone resorption
It is second criterion that predicts valid alternative approach to long conventional implant for the rehabilitation of posterior atrophic maxilla. There were 18 studies[45],[46],[47],[48],[49],[50],[51],[52],[53],[54],[55],[56],[57],[58],[59],[60],[61],[63] included for the meta-analysis. There was no significant difference in MBR for both short and long implant. However, the MBR was less for short implant marginally. Esposito et al.[47] and Esposito et al.[57] reported higher bone resorption for long implant. The factors which influence on MBR are implant diameter and crown implant ration at implant level and bone density, submerged healing at the tissue level and patient smoking habit. The implant diameter mentioned in the review was ranged from 3.7 mm to 8 mm, majority of the studies were used the diameter between 4 and 6 mm except Bechara et al.[50] was used 8 mm diameter implant. The present review, findings of MBR between short diameter implant and long diameter implant does not show any significant difference. Bechara et al.[50] reported the negative correlation between implant diameter and MBR. The proportionate increase in the diameter to compensate the length of the implant does not show much benefit as the osseointegration already occurred before the prosthetic loading.[83]
The C/I ration in the present review only three studies[45],[53],[61] recorded C/I ratio. However, the radiographic appearance presented in the studies observed more C/I ratio for short implant, but there was no significant difference in bone resorption between short and long implant. A similar observation was also mentioned by the studies[45],[53],[61] that recorded C/I ratio. Hence, both the short and long implant satisfy the Albrektsson criteria of bone resorption.[84] The retrospective cohort findings regarding C/I ratio reported the range of C/I was 0.5:1–3:1. The mean C/I ratio of implants in function was 1,3:1 and the mean C/I ratio on failed implants was 1,4:1.[85] Increasing the length of the implant to compensate the crown height does not show much influence on stress distribution, as the angle of the implant generates the magnitude of the stress at the peri-implant crest area, more the pronounced implant angle, greater will be the bone resorption and the diminishing toward the implant apex.[86] Photo-elastic analysis reveals that crown space is more significant than C/I ratio.[87] Moreover, increase implant length corresponds to increase crown height result will be more prosthetic complications, due to increase lever arm.[88]
Bone density is the well-established evidence for primary implant stability. However, the bone at posterior maxillary ridge has more cancellous marrow and less trabecular portion of bone.[89] The review mentioned the height of the remaining bone was ranges from 4 to 9 mm. The justification of short implant is more viable in type IV bone density[90] as the cancellous bone offers rapid modeling, due to highly vascularized and less fatty marrow.[91] The rough surface implant along with adaptive remodelling of cancellous bone produces radiographic density and achieved implant initial stability.[92],[93] Finite element analysis observations confirm the fact that short implant induces more stress on trabecular bone; therefore, more density changes occurred at short implant.
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