Predictable management of combined atrophy
Narrow (3.3 – 3.5 mm) short and extra-short implants

Short and extra-short implants are an increasingly common treatment option for vertical atrophy of the maxilla and mandible with similar or even better predictability than regenerative techniques aimed at regaining lost bone volume in order to place implants of normal length [1-3].

Narrow implants are a similar alternative to short implants, but in this case for the horizontal resorption. Their size and designs have evolved over time. Currently, according to the classification of Klein, Schiegnitz and Al-Nawas (2014) [4], those implants with a diameter of less than 3.5 mm are considered as narrow. Narrow implants can be categorized as:

• category 1 (implants narrower than 3 mm), 
• category 2 (implants between 3 and 3.25 mm in diameter) 
• category 3 (implants between 3.30 and 3.50 mm in diameter) [4–5]. 

Systematic reviews evaluating the survival of narrow implants (less than 3 mm) showed a survival rate of more than 90 % with a follow-up period of one to three years and a higher survival rate (93.8 %) for implants with diameters between 3 and 3.25 mm with a follow-up period of one to five years [6–10].

In most studies with these reduced-diameter implants, their length was regular to achieve good anchorage of the apex and thus adequate primary stability. More recently, the use of narrow and shorter implants has been validated in the literature. A review published in 2018 found that implants shorter than 7 mm and narrower than 3.5 mm had similar survival rates compared to regular-length implants. Marginal bone loss was 0.5 mm after three years of follow-up [11].

Other studies published on this topic reported similar results. However, there are only a few studies on this topic [12]. 

In this paper, we present a series of clinical cases of patients treated with reduced-diameter (3.3–3.5 mm) and reduced-length (6.5–7.5 mm) implants.

Materials and methods

Consecutive patients were retrospective-ly selected from those treated in a private clinic (Vitoria, Spain) from 2017 to 2018 who met the following inclusion criteria:

• over 18 years old
• horizontal atrophy in the maxillary and/or mandibular posterior region with residual bone volume between 4 and 5 mm, with both buccal and lingual cortical preserved
• vertical and horizontal combined atrophy with a residual bone height between 6.5 and 8 mm.

Before implant placement, antibiotic premedication consisting of amoxicillin 2 g (orally one hour before surgery) and paracetamol 1 g orally (as analgesic) was administrated. Subsequently, patients received amoxicillin 500 – 750 mg orally every eight hours (depending on weight) for five days. After intraoral examination, treatment planning was based on diagnostic models, radiographs (CBCT) and special software (BTI-Scan III).

All implants were placed by the same surgeon and subsequently followed up by two dentists. The surgical technique was the same in all patients and consisted of anesthesia, elevation of a full thickness mucoperiosteal flap, and bio-logical drilling of the implant bed with low revolutions (50 rpm).

Data collection was performed by two independent examiners (different from those performing the prosthetic or surgical phase). All the data were compiled in a database and analyzed with a statistical analysis software.

Patients were checked every six months using panoramic radiographs or intraoral radiographs with positioner. The bone level was measured after calibration (based on the known implant length) using a special software (Sidexis measure and Digora).

Statistical analysis

The main variable studied was the im-plant survival, and the secondary variables studied were the crestal bone stability, the prosthetic complications and the prosthesis survival. The patient was the unit of measurement for the analysis of age, sex, and medical history. A Shapiro-Wilk test was performed to confirm the normal distribution of the sample.

Qualitative variables were described by frequency analysis. Quantitative variables were described by the mean and standard deviation. Implant survival was estimated using the Kaplan-Meier method. All analyses were performed with SPSS v15.0 (SPSS Inc., USA) and the significance level was set at 5 % (p < 0.05).

Results

14 patients (all female) were included and 14 implants met the inclusion criteria. The mean age was 63 years (± 3.45). Two patients were smokers. All treatments were performed in two surgical sessions. The diameter of the implants was 3.3 mm in 42.9 % of the cases and 3.5 mm in the rest. In terms of length, the implants placed were 6.5 mm in 14.3 % of the cases and 7.5 mm in the remaining 71.4 %. Graph 1 shows the distribution of the implants included in the study in terms of length and diameter.

The most common location of the im-plants was the lower first molar (28.6 %), followed by the second upper molar (14.3 % of the cases). Other positions had a similar frequency as shown in graph 2.

During the follow-up time, none of the implants studied failed. The mean follow-up time was 3.5 years (± 5.2) with a range between 2.5 and 4 years.  The mean mesial bone loss was 0.31 mm (± 0.10) and the mean distal bone loss was 0.15 mm (± 0.88 mm). All implants were rehabilitated with screw-retained prostheses using transepithelial and metal-ceramic crowns.

Images 3 to 9 show a case included in the study.

Discussion 

In cases of severe vertical mandibular atrophy, where the placement of dental implants is required for the proper functional rehabilitation of the patient, various bone augmentation techniques are used to allow implant placement.

Short and extra-short implants are a safe option for the rehabilitation of the posterior region of the maxilla and mandible as an alternative to more complex bone augmentation techniques with long-term survival rates of over 98 % [13–17]. Even with narrow implants, the survival rate is between 90 and 94 % ac-cording to published studies. However, when separated from the expansion and/or regeneration techniques that usually accompany these implants, the survival rate is higher, reaching 100 % in some studies [19–22].

As mentioned above, the main advantage of these two groups of implants is that a costly regenerative procedure for the patient can be avoided. Also, it ensures less traumatic surgery and less morbidity for the patients [11].

Conclusion

Short and narrow implants are a minimally invasive alternative for the treatment of combined vertical and horizontal atrophy.

EDUARDO ANITUA