Immediate Loading of Short Implants in Posterior Maxillae: Case Series.

BACKGROUND: There is an increasing number of scientific evidence supporting the clinical use of short dental implants. However, few studies have evaluated the long-term outcomes of immediate loading protocols in short implants. This study aims to evaluate immediate loading of short dental implants in the posterior regions of the maxillae.
MATERIALS AND METHODS: Patients having short implants in maxillae posterior areas inserted before December, 2010 and immediately loaded were selected. The following data were gathered regarding patients' age and gender, implant dimensions, anatomical location, and prosthodontic treatment. The outcome variables were peri-implant bone remodeling and the survival rates of the short implants and the prosthesis.
RESULTS: A 10 short implants were placed in 8 patients. The mean follow-up time was 4.6 ± 1.21 years after loading and 1 implant failed. One prosthetic complication occurred. No prostheses failed resulting in a survival rate of 100%.
CONCLUSIONS: The immediate loading of short implants in maxillae posterior areas could save time, cost and could be regarded as a successful treatment.

Introduction

Since the first publication on immediate loading of dental implants, an increasing number of research and systematic reviews have been published. In 2000, a review of the available clinical and experimental studies have accepted the idea of immediate implant loading and have recommended the type of fixation that minimizes the implant micro movements (). The data compiled for the immediate loading have shown a similar implant survival as delayed loading (-). The insertion torque is one of the most influential parameters in the treatment success (-). When standard-length implants are used, the scientific evidence indicated the absence of significant differences between functionalization protocols in terms of implant survival and peri-implant bone remodelling (). However, the anatomical location of the implant is a factor that could affect the survival of dental implants and prostheses. Immediate implants with immediate loading have a higher failure rate in posterior areas than in the anterior areas when estimated together in different published studies (0.54% - 0.45% respectively), (). The implants in the maxilla have more failures than in the mandible ().

The use of short dental implants may limit the needs for bone augmentation. The predictability of short implants has been assessed in a recent survey of randomized clinical trials of implants placed in augmented sinus (). Short (length ≤ 8 mm) implants have presented a predictable survival rates and have resulted in three times lower intraoperative complications compared to long implants (). Short implants placed in a posterior partial edentulous region have presented a high initial survival rate, which is similar to long implants (). As mentioned above, shorter dental implants may represent the preferred treatment alternative in atrophic alveolar bone since they have been associated with lower biological complications, decreased morbidity, costs and surgical time ().

Many clinical questions were raised regarding the predictability of immediate implant loading and short implants. For example, the logical question was whether the immediate loading of short implants is predictable as well. In order to answer the question, short (≤8.5 mm) implants have been immediately loaded and periodically assessed. The null hypothesis was that immediate loading has no effect on the survival rate and marginal bone stability around short implants inserted in maxillary posterior areas. The implant survival rate and peri-implant osseous remodeling, complications and survival of the prosthesis were assessed.

Materials and methods

STROBE guidelines were followed for the preparation of the manuscript (). The study was performed in a dental center in Vitoria, Spain. The inclusion criteria in this retrospective study were:

Age higher than 18 years.

Placement of short BTI implants (length 7,5 - 8,5 mm) before December, 2010.

Implant inserted in maxillae posterior areas.

Immediate implant loading.

To assess the principal outcome, implants were followed clinically and radiographically with panoramic radiographs to identify any implant failure. A failure event was defined as the absence of the dental implant in the patient mouth at the time of evaluation. Peri-implant bone remodeling was measured by assessing the difference in the position of the marginal bone (in relation to implant platform) in the most recent radiograph and its position at the time of implant loading. The implant length was used to calibrate the linear measurements (Sidexis, Sirona, USA). The Shapiro-Wilk test was selected for testing the normality of data. The one-way ANOVA analysis was used to indicate the effect of the antagonist type on the marginal bone stability.

Surgery

The plan of treatment was set after clinical examination and the study of the diagnostic wax-up and cone-beam computerized tomography (CBCT) scans. A surgeon prepared the implant site using a low-speed drilling procedure (125 rpm) without irrigation and the diameter of the last bone drill was determined according to the bone density (obtained from a CBCT scan), (, ). Plasma rich in growth factors was used to enhance the osseointegration of dental implants (PRGF-Endoret®, Biotechnology Institute BTI, Vitoria, Spain). For placing the dental implant, the surgical motor was set at 25 N/cm2 and the implants were finally seated manually by a calibrated torque wrench. Transepithelial abutments (Multi-Im, BTI Biotechnology Institute, Vitoria, Spain) were subsequently immediately placed. A prosthodontist performed the prosthetic rehabilitation of the patients. Impression copings were placed and an impression was made with polyether impression material (Impregum Penta; 3M ESPE) and the open-tray technique. A screw-retained temporary fixed prosthesis was then placed during the first 48 hours after implant placement. The definitive fixed prosthesis was delivered once the stable peri-implant soft tissue was achieved. The follow-up check-ups were at 1 week after intervention, at 1 month, at 3 months, at 6 months, and from that moment ahead, once a year.

Follow-up and evaluation of success

Implant success was defined according to the criteria suggested by Buser et al () and modified by Albrektsson et al. (). Survival of the implants was defined by the presence of the implant in the mouth at the end of the follow-up period.

The implant-supported prostheses were screened for the occurrence of technical complications. The criteria proposed by Lang et al () were followed to assess the prosthesis.

Statistical analysis

The data were collected and analyzed by two independent dentists. Absolute and relative frequency distributions were calculated for qualitative variables and mean values and standard deviations for quantitative variables. The Shapiro-Wilk test was selected for testing the normality of data distribution.

Kaplan-Mier method was used to assess the survival of the prosthesis and the implant.

Results

Eight patients with 10 short implants in maxillae posterior areas participated in this study. All implants were inserted by the same surgeon. Subsequently, they were immediately loaded by provisional prostheses with screw prostheses and multi-im abutments. The patients' mean age was 65 ±5,9 years (range: 55 to 74 years) at the time of surgery and 70% of patients were females. One patient was a moderate smoker.

The short implants had a length of 7.5 mm (3 implants) and 8.5 mm (7 implants) (Table 1). The insertion torques were ≥ 30 Ncm in all cases. The implants were followed for 55,5 ± 14 months (range: 18 to 69 months). The implants were followed for ≥ 4.5 years for 9 (90%).

Table 1

Lengths and diameters of implants

Diameter (mm)	Length (mm)		Total
	7.50	8.50
3.75	0	2	2
4.00	1	2	3
5.00	3	0	3
5.50	1	1	2
Total	5	5	10

One implant failed after 5 years of loading. This implant was replacing the tooth #45.

The cumulative survival rate of immediately loaded short implants was 90% (Figure 1). There was no failure at the prosthesis level.

Figure 1

Cumulative survival rate of implants

The periimplant bone stability was assessed after 54 ± 16 months of loading. The mean of mesial bone loss was 0,35 mm (+/-0,73; range 0,41-1,40) (Figure 2) and the mean of distal bone loss was 0,93 mm (+/- 0,54; range 0,23-1,81) (Figure 3).

Figure 2

Mesial bone loss

Figure 3

Distal bone loss

The prostheses were of metal-resin for 9 short implants and of resin for one implant. The provisional prosthesis was replaced by a definitive one after 12 ± 3 months (range: 4 to 20 months) of loading. The definitive prostheses were all screw-retained in all patients and all of the implants were splinted to other implants (one or more) ().

Figure 4

Final prosthetic apliances

The opposing dentition were natural teeth (restored and unrestored) for 3 and implant-supported prostheses for 7. The one-way ANOVA analysis showed the absence of an effect of the antagonist type on the marginal bone stability.

Discussion

The immediate loading of short implants in the maxillary posterior areas has no negative effects on implant-supported prostheses.

Cannizzaro et al have reported the 4-year outcomes of immediate Vs early loading of 6.5 mm long single implants in a controlled randomized split-mouth clinical trial (). The insertion torque was > 40 Ncm in both groups. The implant success rate was 96.7% for both groups. In another randomized controlled clinical trial, the 1-year outcome of immediate loading of 5 mm long implants by a fixed cross-arch prostheses have been compared to those of 11.5 mm-long implants (). The insertion torque of most of the implants has been > 50 Ncm. Only one failure has occurred. The differences have not reached the statistical significance. In a recent study about the rehabilitation of edentulous maxilla, the survival rate of an immediately-loaded short implants (length between 7.0 and 8.5 mm) has been 95.7%.21 However, most of the implants (68 of 74 implants) have been placed at the position of the lateral incisor (). In our study, the implants have been placed in posterior maxillae areas, that is a worse localization, and the survival rate of implants was 100%% ().

Excessive trauma and thermal injury during implant socket preparation have been considered to be critical for implant success (, ). Implant site has been prepared by low-speed bone drilling without irrigation. This drilling protocol has not caused overheating of bone (, ). The good quality of bone particles resulted from the drilling at low speed, thus confirming the absence of bone damage (, ).

In this study, the mean periimplant marginal bone loss around the immediately loaded short implants was less than 1 mm. Immediately-loaded short implants have lost 0.4/0.5 mm less marginal bone than the long implants (up to 1 year follow-up), () In another study, the 3-year marginal bone remodeling for short implants was 1.25 ± 0.99 mm ().

The present study has some limitations regarding data, and the absence of randomization or blinding.

Conclusions

The immediate loading of short implants inserted in posterior maxillae areas, supporting a multi-unit prosthesis, has not jeopardized either the implant success or the marginal bone loss. Taking the measurements which would increase the implant primary stability and minimize implants micro-motions could contribute to the observed outcomes.